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mightybg

Esc Circuit

Question

I am troubleshooting the ESC circuit. I have done continuity checks from the knock sensor wire to the ecm and it is good (0.5ohms). The engine running voltage unplugged is 4.86v(good I think). the problem i have is that if i leave it unplugged I am not getting a code43. I have driven the truck with the connector disconnected and I do not get a check engine light at all. I have a re-man pcm in the truck and it is the right one (16147060). Can this be caused by my memcal/PROM?

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I can't say I can answer your question but it might help us out if we know what you are working on. Year, make, model and engine if not a vin.

 

Edit: Also what is the original complaint that led you down this road? Was it that you unplugged the sensor and no light came on, or did some other symptom make you think to unplug it and start checking.

 

1991 chevy k2500, 5.7l

the truck was running poorly vacuum would go low the more load you put on it and it stumbled at idle it ran hot etc. The previous owner had gotten "creative" on an engine rebuild i think and when he put the truck back together not everything got hooked up as it should. I have been repairing many bad things on theis truck for 2 years. cam shaft was worn on #5 cylinder the heads were plugged distributor was about to fall apart and the o2 sensor was wired to the knock sensor blue wire and there was no knock sensor on the engine at all. the o2 connector was laid on top of the transmission i gues this is why he missed it and hooked it the the closest wire he could find. I have almost got it running good but not chevy 350 good. I was checking the things that cause overheating and poor vacuum and figured out that the knock sensor i put on the engine was not the right one( the one that belongs on the truck has the white connector). so i was wondering why i didn't get the 43 code. so i unplugged it and drove it around for a couple of days and never got the code 43 or check engine light. I did continuity and voltage checks on ckt 496, Knock circuit, and it was good. the truck currently runs a little rough low power and overheats a little. I was running after putting the heads back on once and when i accelerated heavily of a corner the truck all of a sudden got a shot of power and then the CEL came on and the code 43 was stored. so I again checked the knock circuit and tested it with it unplugged running at normal temp and again no code 43 or check engine light. I have corrected a lot of things on this truck and I want to eliminate this problem or maybe this is the fix for all my problems. I have checked or replaced everything else on the truck, I can list all the things I have changed if it would help you help me. any help at this point is greatly appreciated.

 

items replaced or checked:

entire ignition system (plugs, wires, coil, distr, control module)

fuel system (pump regulator filter injectors)

TPS o2 sensor

timing chain

cam and lifters

exhaust componenets( muffler and cat)

intake

valve springs

egr and egr solenoid

map sensor

coolant temp senders

checked compression ( all 160-165)

fuel pressure is 12psi

the ecm (16147060 L05 engine with 4L80e) used the same old prom

alternator

vacuum lines and check valve for booster

pcv system

checked thermostatic air cleaner

new water pump fan clutch and radiator

just about everything

and I don't hear any knocking coming from the engine, I don't think i mentioned that. I have not put the correct knock sensor on yet I was waiting to figure out why the "tests" for the knock circuit weren't giving a check engine light.

I replaced the Idle air control valve and ignition switch also.

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Wow that's a whole lot of post. I'm going to assume you have diagrams that I don't have because my 91 diagram book has long since been lost. It looks like the code might not set if the ESC module ground circuit is not good but that's just a guess I would have to do some experimenting to know for sure. If memory serves that would be the ground that belongs on the thermostat housing stud but don't quote me on that. Easy knock sensor diagnostics, hook up a timing light and watch to see if your mark moves around when you tap the block around the sensor area. If it works move on because I'm not sure why it won't set.

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You ain't kidding i have spent ALOT of money on this thing. I started to become a "I'm not going to let this truck beat me I'm going to beat it" thing. the voltage on the sensor ckt was 2.2 with it connected. The vacuum was low until I changed the valve springs and then it would bounce low every once in a while and it was bouncing. I found that #8 cyl was not getting good combustion due to a poorly sealed port on the top of the intake (the 1/4" npt port on top that goes to the number #8 intake runner). after that it started running smoother. It just didn't have the power i thought it should and I was still pessimistic about the temp rising a little when sitting at idle. Long story short, and I know this may frustrate you a little since you have spent a lot of your time helping me, but I sold it. the guy that bought it said he thinks it is a transmission problem with the first shift solenoid. I guess that may make it feel like it doesn't have power but I am not so sure. any ways it is someone who is getting a fresh start at troubleshooting it and it was getting old for me and he needed a truck and I was willing to sell one. but seriously thanks for all your help and time. I actually think i had it running like it should be but had been fixing things for so long on it that I was still looking for problems with it. I am moving on to my other toys a 1966 gmc truck and 1991 jeep wrangler who will be getting a LT1 from a Impala SS. they got neglected cause i spent the last 2years working on the stupid work truck. So, Truck 1 Brian 0.

one more thing One of the terms of sale was if he got it running like a top he had to tell me what was wrong with it. so I will post it.

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Wow that's a whole lot of post. I'm going to assume you have diagrams that I don't have because my 91 diagram book has long since been lost. It looks like the code might not set if the ESC module ground circuit is not good but that's just a guess I would have to do some experimenting to know for sure. If memory serves that would be the ground that belongs on the thermostat housing stud but don't quote me on that. Easy knock sensor diagnostics, hook up a timing light and watch to see if your mark moves around when you tap the block around the sensor area. If it works move on because I'm not sure why it won't set.

 

i checked the ecm grounds I have mine on the intake bolt/stud real close to thermostat. I ran a bunch of extra grounds to be sure grounding wasn't an issue. I did a check to see if the knock circuit was partially grounded and I got 4.7kohms to ground I assume i am reading the impeadance of the sensing circuit in the ECM. I was wondering if when the O2 sensor was hooked to the knock circuit if it caused damage. I called bosch and they said the 5volt reference on the O2 sensor would not damage it. I have thrown so many parts at this thing eventually i will break this problem or it will break my bank!lol I was just wondering if the prom would cause it not to pick up a failure or if the knock circuit error was triggered from the ECM. My AllData information only tells me so much. I am certain the truck is mechanically sound I just have a squirrelly electrical problem.. Oh, I forgot to mention which is kinda a major concern too is when i hook up a laptop to the diagnostic port there is a bunch of noise on the comms until I get above a certain RPM and then the comms errors will quite down. the truck runs good for the most part before it warms up and goes closed loop.

thanks for your help.

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I was just wondering if the prom would cause it not to pick up a failure or if the knock circuit error was triggered from the ECM

I can only guess that the answer would be no. I have never had a prom do anything like that. The prom is for vehicle specific data. The diagnostic functions are handled by the pcm itself.

 

My AllData information only tells me so much

 

Don't knock AllData, if you have it you are looking at more info that most dealers have on anything older than 97.

 

 

. I am certain the truck is mechanically sound I just have a squirrelly electrical problem.. Oh, I forgot to mention which is kinda a major concern too is when i hook up a laptop to the diagnostic port there is a bunch of noise on the comms

 

The comms issue thrown in there would make me exhaust almost every ground test in existance before I got too crazy about anything else. You said you checked the pcm grounds but not how you checked them. Continuity checks don't get it, a single good strand of wire will show minimal resistance but it cant carry a circuit. Do you know how to do a loaded circuit test? I would map out where all the powers and grounds are in the pcm and do loaded tests (WITH THE PCM DISCONNECTED) to each of those circuits.

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"I'm not going to let this truck beat me I'm going to beat it"

 

This is how I have made plenty of paychecks go bad but I still can't let one beat me.

this may frustrate you a little since you have spent a lot of your time helping me, but I sold it.

 

Not at all, I half come here to learn and help and half to keep my self sharp on things I take for granted or just forget. I spent my free time in the shop last week doing voltage drops and playing with vacuum because I always forget how much vacuum can tell you. We don't use it very much anymore.

 

I actually think i had it running like it should be but had been fixing things for so long on it that I was still looking for problems

 

I feel ya on this, I refuse to road test one of my allignments, no matter how straight everything is I swear the steering wheel is off by at least two degrees.

 

Glad you got rid of your problem one way or another, sometimes making the whole vehicle go away is the way to go...I hate when they beat me though :crackup:

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Ok plug it in and recheck voltage once in closed loop. It should be about 2.5 but back to the old down and dirty test though, did you hook up a timing light and tap on it while watching the light. If it moves the system is working and I wouldn't get too jazzed up about why it doesn't set a code when we think it should. If it doesn't move we can go down that path.

You have diag software you said right. Does it have any way to snapshot? If so can you send it? If not can you tell me what you have for a block learn once it starts acting up.

 

You have no codes right now right?

 

You said poor vacuum, what is it at? Is it steady or fluctuating?

 

The converter is new but how new. If it was something you replaced early on unburned fuel can kill one quick. Can you check backpressure? Even if you replaced it last it would make me feel good if you could check that.

 

I know you want to go down the electrical gremlin road but it can be the "garden path". An old instructor used to say that all the time, the garden path is pretty and makes you feel good but it can lead you into the abyss.

 

When something is kicking my ass I usually find something I missed on the fundamental side. Knock the block and watch the light, if the mark moves get off the "why doesn't the code set" garden path. You probably know block learn is the addition or subtraction of fuel in closed loop, it can tell us alot. Backpressure will cause low vacuum and knowing that can tell us something if not at least to elliminate something.

 

I could be off but it looks like you have spent a bunch of money, I'm just asking you to waste a little time if I'm off.

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Doh, well that would explain my confusion. I was looking at the diagram for a 4L60 that circuit looks way different, everything goes through the esc module on that one and wire dangling would not set a code unless the test ran. To answer your original question according to the diag table yes a mem-cal can cause an issue. With the sensor plugged in, engine running you should have around 2.5 volts @ the PCM ckt 496 to ground. You said you had something like 4.8 but I don't think you said weather the sensor was plugged in or the vehicle was running.

 

4.88 volts was with the sensor unplugged.

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I checked the ground using continuity once when the wiring harness was out of the truck and at this time I physically checked the wires for breaks or bad spots. with the harness installed I checked voltage from the the chassis and engine to the negative batt terminal. with the engine running i back probed the ecm connectors and checked voltage from the d5 (knock circuit term) to the ecm case and had 4.88volts. i shut the truck off and back probed the c2 and c3 term to the ecm case and had continuity. I have not load tested the wires and I don't know how to. how difficult is it? the fact that I have 4.88 volts on the knock circuit for way longer than 16sec (alldata) and no 43 code does not give me any confidence i the ecm. the knock ckt test for voltage above 4.6v is to determine if there is an open ckt which would be no ground path for the ckt. and the 4.88 volts referenced to the ecm case should set it off. with connector dangling in the wind with the truck driving down the road shoudl give me a 43.

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I can't say I can answer your question but it might help us out if we know what you are working on. Year, make, model and engine if not a vin.

 

Edit: Also what is the original complaint that led you down this road? Was it that you unplugged the sensor and no light came on, or did some other symptom make you think to unplug it and start checking.

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Doh, well that would explain my confusion. I was looking at the diagram for a 4L60 that circuit looks way different, everything goes through the esc module on that one and wire dangling would not set a code unless the test ran. To answer your original question according to the diag table yes a mem-cal can cause an issue. With the sensor plugged in, engine running you should have around 2.5 volts @ the PCM ckt 496 to ground. You said you had something like 4.8 but I don't think you said weather the sensor was plugged in or the vehicle was running.

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