No Fuel Pressure Troubleshooting Basics (any car)
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- čas přidán 9. 12. 2016
- How to troubleshoot a no fuel pressure problem on any car. Is it the fuel pump, relay or wiring? Computer problem? Cam or Crank sensor problem? These questions and many others I will answer in this video.
The car being tested is a 2001 Ford Explorer with a P0231 Fuel Pump Secondary Circuit Low trouble code.
Engine Performance Diagnostics chapter 15
Symptoms
- no start
Fix
- replace faulty fuel pump relay
Tests shown
- how to test fuel pressure
- how to use the check engine light during cranking as a guide
- how to use the tachometer during cranking as a guide
- how to test a fuel pump relay
- how to determine load and control sides of a relay
- how to determine if the computer is controlling the FP relay
Tools used
- (inexpensive alternative to the scan tool I used) AutoLink AL519 CAN/OBDII Scan Tool w/ live data
www.aeswave.com/cart.php?m=aff...
- OTC 3633 Mini Circuit Tester
www.jbtoolsales.com/otc-3633-...
- S.U.R. & R FPT22 Deluxe Fuel Injection Pressure Tester Kit
www.jbtoolsales.com/s-u-r-r-f...
Related videos
- How to test fuel pressure, injector pulse and spark with basic tools - Honda • How to test fuel press...
- Fuel pump electrical circuit diagnosis (no fuel pressure testing) GM • Fuel pump electrical c...
- How to test an electric fuel pump (no fuel psi testing) Ford
• How to test an electri...
- Fuel Pump Electrical Circuits Description and Operation
• Fuel Pump Electrical C...
Playlist
- (Chapters 14, 15,16) Fuel Delivery and Fuel Pressure Testing
• (Chapters 14, 15,16) F...
For more information on this topic, I have written a “field manual” called Engine Performance Diagnostics which is available at www.scannerdanner.com as an eBook or paper book.
Want even more diagnostic training? Whether you are a DIY trying to fix your own car, someone looking to become an auto technician, or a current auto technician that wants to get more into diagnostics, subscribe to ScannerDanner Premium www.scannerdanner.com/join-sc... There is a 14 day free trial.
On ScannerDanner Premium I will bring you right into my classroom at Rosedale Technical College. You will find page for page lectures taken right from my book as well as exclusive classroom type case studies. What is so special about these classroom case studies? I pull live problem vehicles directly into my classroom and we troubleshoot them in real time, using and applying the theory and testing procedures we learn during the classroom lectures. There is no better on-line training of how to troubleshoot automotive electrical and electronics systems anywhere!
Disclaimer:
Due to factors beyond the control of ScannerDanner LLC, it cannot guarantee against unauthorized modifications of this information, or improper use of this information. ScannerDanner LLC assumes no liability for property damage or injury incurred as a result of any of the information contained in this video. ScannerDanner LLC recommends safe practices when working with power tools, automotive lifts, lifting tools, jack stands, electrical equipment, blunt instruments, chemicals, lubricants, or any other tools or equipment seen or implied in this video. Due to factors beyond the control of ScannerDanner LLC, no information contained in this video shall create any express or implied warranty or guarantee of any particular result. Any injury, damage or loss that may result from improper use of these tools, equipment, or the information contained in this video is the sole responsibility of the user and not ScannerDanner LLC. - Auta a dopravní prostředky
![New Fuel Pump - Still No Fuel Pressure - Now What? [2012 Ford E350]](http://i.ytimg.com/vi/GJ9O8pTkK4w/mqdefault.jpg)
This is far best CZcams videos I see out there most of all the videos just want to show you need to get a fuel pump
Excellent. Your channel has become my goto place lately. Always understand cars much better after watching your videos. Big thanks from irish tech here.
Thank you!
I'm glad you pointed out that the pump prime operation is independent of the running pump control.I did not know that
Nice, sweet and simple , video flows along a a good pace.
Paul I keep meaning to PM you but any time I am on the Forum I get distracted reading threads.
It's great to know how to use a scope, and sometimes, a scope is an invaluable piece of equipment! But, a lot of circuit diagnostics can be done with a test light and a DVOM. Circuit design knowledge is the best tool!
Awesome stuff, Paul!
Thanks brother
Great vehicle trouble shooting Info, I also have a much better understanding of electrical relays that can be found in so many other non automotive applications as well. Thank you for the extremely helpful knowledge!
I fixed my buddy's 96 explorer with that same issue. It feels great talking about how I watch Scannerdanner and apply his techniques. Thank you . Merry Christmas Mr. Danner.
Merry Christmas to you too brother. Thank you
Great video Mr. Paul you're the best teacher no one explain like u do man THANKS
Thanks so much!
I have a 99 Mountaineer which is similar to the Explorer. When you mentioned the code FP Secondary Circuit Low I knew right away it was either the relay or a wire harness problem. I've studied the FP circuit on my truck, creating faults and taking voltage readings when I have time on my hands. My FP circuit should be similar to the Explorer in which my truck has a bias voltage of 6.8 volts that goes to a splice to the #5 load side contact, IFS and FP with the KOEO. The bias voltage is used for diagnostics and it will flag a code if the ECM doesn't see the right voltage. I know all this stuff because of you Paul so thanks again!
Thank you so much Charles!
just got you a new sub for how great you explained everything thank you 6 years later
Thanks for the sub!
I really appreciate the detail and knowledge you share. Most helpful carguy I've come across on youtube.
I appreciate that! Thank you Berend van Rossum
Excellent as always man, especially the relay circuit checks!
Star Wars could you put the
At 6:41 I swapped the relay with a known good. (Faulty relay). The rest of this video is how to test the circuit IF the relay was NOT bad
Merry Christmas Danner to you and your wonderful family
Man I'm glad that you exist.
First, let me say that I love your videos. They are very informative and easy to follow. You have gained a fan here for sure. I wanted to make one quick clarification concerning the relay diagnosis. If I'm not mistaken, you mentioned the power lug or the side that is "hot all the time" in the relay box as being the "Load" lug. Actually that is considered the "Line" side that is hot all the time. The "Load" is whatever device is drawing power from it. This may be penny ante info but it can make a huge difference in repair work in A/C and D/C power systems. Anyway, keep up the good work and thanks for your time and energy to make these videos.
We don't use the terms lug and line on the DC side of things in this field anyway. But thanks!
Thanks Paul another great video , big thanks from the uk
I just bought the test light using the link you gave in the description! Happy Hanukah!
Nice! Happy Hanukkah to you too my brother
This video helped out alot. Keep up the good work.
I learned so much from your videos, thanks for do it
dude, you are way too good!!! fun and educational
Thanks a lot for such great information.
Great video Paul.
Wicked I'll check this as soon as I get some daylight thanks!
Thanks for this video brother. Thanks for everything.
Thanks scanner dan you explain thing to where people that work on their own car easy..
Excellent Paul.
awesome, right to the point and very simple.....
Wicked subscribed thanks for the solid video
excelente diagnostic. testing. amigo.
Great teach, Paul
Good job man. Love it when a plan comes together 😄 it's amazing a few places I've worked in don't even have fuel pressure testers. Here in uk big expensive tools like that are bought by the garage owner normally
thank you my friend
Paul, I have found underneath the under hood fuse box, corrosion built up on terminals that have had the burnt relay scenario.
Great video thanks for the info!
Good content as always Paul
Thanks brother
Nice that you didn't have to get under the truck as usual. No rust in the eyes or fuel to the armpit.
but thats how you know if you have good flow :)
arielatom03 87 octane deodorant.
Great information thanks.
something to watch out for with fuel pressure gauges, which I learned the hard way, don't mix up the hoses from a different set, the fittings are not always the same and they don't press the Schrader valve in the gauge, so therefore the gauge stays at zero when you crank. the fittings for Mac gauge hoses are a little bit longer than for the Snap On gauge hose. First time it happened I warrantied the Mac gauge, second time I ended up buying a new Snap On gauge and it worked, but when I was swapping over some fittings, is when I discovered the difference.
great video way to go.thanks a lot
I just had to do this same troubleshooting on a '95 Volvo 940 wagon, 206k miles. Long but interesting story ahead ... :)
Complaint was, car would start and run great for the first time of the day ... but then a mile down the street at the first stop, it would shudder and stall, and become a no-start for the rest of the day. Let it sit overnight, rinse and repeat. The poor guy threw over a grand at the problem, but couldn't make it go away. He said he had recently replaced the fuel pump, so I focused on ignition (good example of why testing to verify is IMPORTANT!) - well, I had spark when it was running, and to my surprise, I had spark all the way until it stalled! I could've sworn it was ignition by the way each cylinder seemed to drop out one by one as the engine got hot - like a coil failure. Could clearly hear the fuel pump running, key on, so all the wiring, relay, fuse, computer, and pump was good. Hmmm ... Threw that exact same Actron pressure gauge you had in this vid on there, and saw zero psi! I yanked the pump, grabbed a yogurt container from the wifey and filled it with her nail polish remover (acetone), stuck the pump in there, got some long wires to keep sparks away, and touched the battery I had there in my driveway. Pump buzzed away, but ZERO flow! Not a single drop! I kept on playing with it, and I heard a POP, and had an acetone fountain with a noticeable sound pitch change in the pump. So, it was a bad check valve inside the pump! First time I've ever seen or heard of this type of failure, where it would just block itself up after the pump ran several minutes. Walbro pump too - those are normally pretty good units.
I was relieved - guy had been chasing this problem for over a year, and the car has sat for the past year. Once that pump gets here, she should be a runner. :)
thanks for sharing. learn a lot
You not only know your shit; you know how to communicate your shit. Extreme right of the bell-curve in both regards and have earned a subscribe from me. Look forward to more. Thanks.
Thank you for what you do
It showed for us less tools more intelligency, thanks Paul.
Great video.
Great mechanic
good video sir!
With an inductive load like a motor, coil or AC clutch you get arcing across the relay contacts when the relay turns ON and when it turns OFF. When the motor turns off you also get the inductive kick back (high voltage spike) similar to what you see on the primary of an ignition coil. The arcing across the contacts is what kills the relay, the arcing leaves carbon deposits and pits the contact giving higher resistance (as you said Paul) which causes high temps and failure.
For an inductive load the relay sizing is a bit different, in other words if the fuel pump draws 6A at full load you would not use a 6A DC rated relay. If you look at generic relays you will see a HP rating as well, this is to account for the arcing problem with an inductive load. There are 'snubbers' for the for the load side of the rely to keep them from arcing too.
The only reasons these relays fail with burnt contacts is because it was a defective relay or the manufacturer cheaped out and used too small of a relay (or if they had used a snubber it would have been fine.)
One other thing to watch out for is if the original relay has a snubber built in across the COIL. If it does you have to use a relay with the same type of snubber. The snubber across the coil prevents the inductive kickback from the coil from frying the driver transistor in the ECU.
Great vid thanks
My Guyyyy Keep It Going 💪
Well job 🧑🔧
Awesome. South Affica
I’m impressed n I’m a student that’s interested in your work n I need you help by giving me advice how to repair a clutch pedal coz it’s slippery when I start pressing it... can you please help me with you big fan of ur work
Great info on the engine light going out while cranking telling you there's crank and camshaft signals.
I'm here because I have zero fuel rail pressure on a 2000 Ford Windstar. The ECM is sending the signals just like yours did Scanner and I have swapped a relay as well as tested the old one which was not that old. Still zero pressure. Guess I need to be looking at the fuel pump or wiring going to it to make sure its getting power and ground.
The inertia switch in the right rear jack panel is pushed in but not tested.
That fuel pump is 20 years old so I'm betting it needs a fuel pump.
Ah the good old days of changing a fuel pump on the road and ripping out in a few minutes.
Yes sir, power and ground test at the pump is needed my friend
@@ScannerDanner I was thinking if ground shows up at the relay on the pump wire that you have good ground, it could be shorted though so not 100% accurate. I didn't know which wire was for pump gr at the tank but 12v pos was easy to find with my power probe for prime and cranking. The new pump fixed it.😀
Sure ain't as easy as the old pumps on the motor you could change on the road side. That was my first tank drop job.
Another great video ☺
I ran into a 04 focus that had a malfunctioning pcm relay last week. I tested for battery voltage and resistance to ground on the control. it had had a high resistance on the ground and a bad relay. this caused a no crank situation do to no pcm ground on the starter relay.
good video
Thanks
I've got the same problem at the moment but not sure which is the rely, the ones I thought it was with 404 on the top I've changed them for brand new and it's still not starting... car is a 2010 facelift seat leon mk2 2.0 tdi cr fr 170bhp
thank you very much I can any car testing
Yes, there are some differences car to car. Watch the videos I have listed in this description on this video
I'm here because Eric the Car Guy just said Scanner Danner's school (Rosedale Tech) is the one of the best!!
Thank you! And tell my buddy Eric I said thank you too!
I guess I'm going to have to get your book for Christmas
Thank you! Merry Christmas
I’m not getting any power or prime to fuel pump.
The float does read on gas gauge...
Any ideas?
Best video easily on CZcams. Question, when you turn the car to the on position do you in the video hear the fuel pump prime with no pressure ? Because I can hear mine prime but still no pressure.
Not all systems will give a prime, but if you do hear one, that is a good indication that your pump is getting a power and ground. I'd still recommend checking them before making the call on a bad pump.
@@ScannerDanner ok thank you for the tips I appreciate it.
citroen c4 year 2012. 1.6 diesel. was driving then cut out. modules saying no comms with engine ecu.. autel live data showing 0 mbar fuel pressure even when cranking and with foot to floor engine starts badly. clicking sound coming from right side of engine too.
what would you do next..?
Hey bud, you’re an absolute genius. Crazy smart at diagnosing. Love your vids. If there’s any way you can help me. Car won’t start, then it will, then I’ll turn it off, then it won’t start, then it will, then it won’t for about 15 times, then it will start consecutively for about 15 times. Over and over back and forth intermittently starting. Tried diagnosing it, unfortunately I’m not too advanced at diagnosing. Alternator is new. Just changed all spark plugs and wires. Ignition coil is good. Battery is new. The engine wire harness that plugged into the ignition coil was bare so I rewired it, put a new connector and wires. Spliced a few of the wires and used a heat shrink butt connector to connect the wires. Then I heat shrinked each wire individually then wrapped them all together in electrical tape together. Changed the camshaft position sensor while I repaired the wires. Don’t know what else it could be. PCV valve is new, don’t see any leaks. The problem first started when I would stop at red lights, it would stall on me. I’d have to start it back up then it would drive and stall again. Did it for a few days until one day it wouldn’t start back up and I was blocking traffic. Got it into a parking lot, opened the hood, took out the fuel pump fuse, put it back in, and it started up. Don’t think that was the problem but I took note of that, that it could be. Just today I went and bought a fuel pressure kit. Connected the fuel pressure gauge to the fuel rail, turned the car onto accessory mode to get the pump to turn on. 0 pressure on the line. Had a friend try to start it, showed no pressure while cranking. After a couple of tries trying to start it, it eventually started and the pressure went up to 39 psi. Now I’m stuck. If you can help I would appreciate it.
So you've confirmed when it does not start, that you have no fuel pressure right? Then the next step is to confirm that you have a good power and ground directly at the fuel pump connection, at the fuel tank, DURING the no pressure problem (so while you are cranking it). If it is good, you need a fuel pump. If it is not, you have a wiring problem. This is a very critical next step. I can help further AFTER this test is done
ScannerDanner I hooked the gauge up to it again today. Ran a lot of tests on it. Yesterday it was showing no pressure on the line at accessory mode. Cranked it and it wasn’t starting yesterday and still showed 0 pressure while cranking it. Got it to start yesterday and it went up from 0 to 39 psi every time it started. Got out there today and it showed 2-4 psi on the line while it was only in accessory mode. Cranked it and this time it started right up, (couldn’t get it to not start to check pressure while cranking again). Pressure went up to 39 psi again. Few minutes later after letting it depressurize itself, I hooked the gauge up to it. Did a on off on off on off accessory mode test on it about 10 times and it showed 26 psi at the end of the test. Cranked it and it started, this time the pressure stayed at 20 psi and dropped down to 18 psi while idling.
@@dylanpaulk7878 as I stated prior, you need to have a voltmeter reading of the fuel pump power and ground when it is NOT starting, when you have 0 or low psi. Everything else is speculation and you know me, I'm not about that. This is our next step. If you have 0 volts at the pump we turn right, if you have 12v at the pump we turn left...
ScannerDanner My dad put the voltmeter on the pump with a paperclip and the car hadn’t been started in a couple days so I don’t if that had anything to do with the battery, but we were skeptical of how to test it properly or which wire was the right wire but we checked both and 1 of them didn’t show anything and the other one showed 10 volts and we didn’t know how to check for ground. I’m sorry we are both learning. With that being said, we installed a new delphi fuel pump. Hooked everything back up, and gave it a fuel pressure test. Still 0 at the rail when put into accessory mode. Pressed in the shrader valve and nothing came out. Primed it and tried to start it, nothing on gauge and no start. Kept going at it and it finally started and pressure was only at 20 psi or 18 psi. Still no difference. Took the hose off the regulator and the gauge didn’t move at all. Went ahead and put in a new fuel pressure regulator. Pressed in the shrader valve and I guess we had to bleed the air out of the line. Fuel sprayed out like never before. Hooked up the pressure gauge, primed it into accessory mode. Took 3 times priming it for it to get to manufacturers psi. Bled the gauge and it went up to 39 psi again. Good to go! So I cranked it and it started right up and it stayed at 39 psi the whole time which was good. Took it on a test drive right after, pulled up to a gas station. Shut it off and came back out. It wouldn’t start. Same issue. Cranked it and cranked it and no start. After 10-15 minutes, it eventually started. Got it home and wondering where to turn now in the diagnosing process or if I should go back and test the wires again ..
@@dylanpaulk7878 Did you get this fixed? I'm so sorry for the late reply. Here is a link for a wiring diagram for your car. You MUST check these wires DURING the no pressure issue. Don't worry about the intermittent nature of this, you just need to do these tests when it is NOT starting eautorepair.adtrk.biz/?a=10817&c=24&p=r&s1=
My 07 dakota randomly wouldn't start last friday and after doing a few tests i bought a fuel pump thinking mine was bad but after dropping my tank i found out mine was still working so i tried injector cleaner and my truck started n ran for the past 5 days but today my truck won't start. I don't have anywhere near as much pressure coming out of the release valve on the fuel rail so do you think my pump is failing or could it be a bad injector?
a scannie on Saturday , sweet
Yeah, I was late on my Friday video. My schedule has been crazy
loved it , it was an unexpected treat . diagnose on.
ScannerDanner Get work from Aleskyfinis
Would that not be a loose female terminal not snuggly connecting to the male terminal on the relay?
I have a problem with my 2008 2.0t FSI. One day I was driving and I had almost no power at all I could barely get up to speed. Then later i tried to start it and It cranks but won’t start, I have low fuel pressure I only have 4 psi. I replaced the in tank fuel pump, the high pressure fuel pump, fuel pump module, and the fuel filter. Do you know what else it could be.
I did a fuel pressure test on mine running rough sometimes..95 Cutlass 3.1...to high 80 psi..any help..the fuel pump is new put in about 3 months ago.. could the new pump just be bad..any help
i lIKE THIS GUY!!!!
Thank you for watching!
hey thanks so much for your videos. You have now fixed two of my old trucks that stumped the stars at the mechanic shops!
Sooo I am trying to buy your book and on Amazon it is listed at a mere 2048$
5 Used from $2,048.03
3 New from $2,265.47
Betcha don;t sell many at that price but then again you don't have to, say only 1000 and your good to go!
I did leave Amazon a message so maybe they will fix it but you need to check it out.
Again thanks for your help!
Haha that's crazy. Go through my website. It's $99 for the paper book and $50 for the eBook.
www.scannerdanner.com
Thank you!
So I know its says any car I bought a new fuel pump put it in no pressure at all replaced fuses and replace old fuel pump fuse but nothing and it's cranking good and everything it's a jeep liberty 03 I like the information you gave on the vid but do you have any thing on a jeep liberty 03 I've done a good amount of your steps but will keep trying love that jeep only 126000 miles on her and believe she has more live just need to figure this out
Great video ,,,what if pump is ok relay is ok but still no pressure ?
Check power and ground directly at the pump connector
What basic scan tool would you recommend for occasional use?
So if u switch relays and do the cuircut test and theres no light then what does that mean? That there is a ground problem?
Great video ! Couldn't you check the coil pack while you were checking for spark as well to see if it was in good working condition before going to the relay, Mr Paul?
It is becoming more and more difficult to answer questions here. I have 80,000 people asking me for help now. So I have created a forum to help you guys better. It is free to join and we can exchange pictures, wiring diagrams and waveforms if needed to help guide you through the process of troubleshooting your vehicle. Thank you so much! Hope to see you there.
Paul Danner (ScannerDanner)
www.scannerdanner.com/forum/post-your-repair-questions-here.html
Hi Paul given a load side pin had gotten hot enough to discolor the plastic in the relay/fuse box, would you suggest also checking the female spade terminal for pin fitment? I changed hundreds of headlight globes and burned up loom plugs in taxi cab headlights and found loose pin fitment in the female terminal a big culprit. Thanks for the videos.
Absolutely and I should have mentioned it but it wasn't the issue here. Good tip, thank you!
What if the engine starts after 3-4 keys then starts on first key throughout the day as normal? Then if left overnight, next morning again it starts at 3rd key?
I had this happen but my issue was a 100% clogged fuel filter, 0 psi at the rail but would still run.
Why wasn't the positive control side always hot on the fuel pump relay? I thought that the fuel pump fuse is fusing the common and positive control side of the fuel pump relay, so if the common was always hot, why wasn't the control side of the fuel pump relay? The PCM relay solved the control ground side of the fuel pump relay when we turned the switch to the on or run positions, this was understood.
Ignition run supplied circuit i believe. Very common to have key on, hot circuits.
Hey Paul when you checked all power terminals to the relay. Is that a method you use on all fuel systems?
Pretty much all relays!
They might have a problem before ... different type/color relay?
My system holds pressure throughout the day, but loses pressure over night. I've changed the the regulator and the fuel pump but still loses pressure over night. (no codes) I prime the system and it starts. Where do I go from here?
Had a Camry with no pump power up sound but had a bad crank sensor could it be Toyota gives you one power up and no crank signal won't give another power. Up ? Threw me off
My 93 town car runs.
But,has no fuel pressure at the rail according to the fuel pressure gauge.
Blows black smoke.
I changed the fuel pressure regulator.
What about if I'm getting spark engine starts up fine but at the Schrader valve it does not show pressure ?
Focus on your fuel pump circuit for sure. But don't be in a rush to put a pump in it. Do some checks!
Great video. Thanks ! Have '08 expedition w/a schrader valve. hooked up a fuel pressure gauge and NO fuel pressure. Car runs fine... I suspect I have the wrong schrader valve adapter. Anyone have a part # for the right adapter?
Just get one that fits a Ford, they are all the same
I connected my fuel pressure gauge to the fuel rail on the Schrader valve and have 0 fuel pressure. I thought I wasn’t connecting it all the way down . But not sure how much more tight it needs to be .
Power and ground checks at the pump would be next
will all 5 pin be layed out the same?
Excellente video, how far are you from West Virginia. I may have a customer for you that's getting the typical lazy dealership runaround.
Pittsburgh PA
someone sifened my gas out my car i put bout 1/2 tank but i can i reprime the pump i did it once when i replaced the pump do i need get more gas i took fuel line off the rail pump ocmes on but no fuel is coming up to the injectors if u cud respond asap plz n thnx
I wish mine was not easy. I've been dealing with my 04 Expedition for over 2 months now, everybody's charging me over $400 to put a fuel pump in it. I put a new one in myself, but I think the new pump is no good because I'm not getting any fuel pressure, but I'm not sure because I'm not a mechanic I'm just kind of one of those weekend warrior and I don't have $400 to pay on a fuel pump job 😭😭
I have a 2003 merc mountaineer, it will run ,but there is no pump priming so it's takes a lot of cranking to start it. Is the prime pump separate from the main fuel pump? Any thoughts.
No the prime is within the programming. Same controls.
What is fuel psi DURING the long crank time you have?
didn't check fuel pump circuit draw??? first always check it has gas. watched people screw around for hours on an empty tank. also seen it started with no pump relay in,seemed it had to crank a long time (reaching a certain rpm before it would start. did this have the pump driver module on the xmember by the spare tire that always rots out??? i get thr feeling this will be back
It started with the relay out only after I got the pump running again. It has 60 psi of pressure as I showed.
A good system holds fuel psi on shut down. It was running off of residual pressure (I even said that in the video)
What's the point of checking pump current draw on this? Burned pins and connectors is always a resistance problem right where it is burnt. It is never from excessive current in the circuit.
Just turn ignition on and listen for fuel pump motor. Will save a lot of what he did in the beginning.
Hi Paul I hope this is not stupid question but how PCM can monitor load side of relay and flag DTC. Thank you. Great video BTW.
Without looking at the diagram, there is most likely a feedback circuit to the PCM that is tied into the pump feed. So if the computer is commanding the pump relay on, it expects to see system voltage on the pump circuit.
Just wondering but how does the computer know that the secondary circuit was low? Sensor wire on circuit somewhere that saw the engine was running and it lost power?
Without looking at the diagram, there is most likely a feedback circuit to the PCM that is tied into the pump feed. So if the computer is commanding the pump relay on, it expects to see system voltage on the pump circuit.