Hi folks... hoping someone can help me with a SES light and Code 43 (ESC knock sensor circuit) problem. The SES light comes on seconds after the engine is started and usually stays on constant; a Code 43 sets every time.

I have followed the Service Manual testing the knock sensors (Code 43 charts on 6E3-A-77) and couldn't trace the problem to being bad sensors. I confirmed 5 volts going to each knock sensor, and resistance on both sensors was within 3.3 and 4.5 K Ohms per the manual. Also, I confirmed 1.5 volts on both knock sensor leads when plugged in which checks. Is it possible to pass these checks but still have a bad knock sensor? The knock sensor wires look fine, and I opened up the ECM and reset the PROM, but that didn't help.

So the charts say it's a faulty knock sensor connection or faulty ECM. I bought two new knock sensors for replacements, but based on the test results, I don't think they're the problem. I've read a number of posts where people replaced the knock sensors unnecessarily.

I replaced the ECM with a Delphi remanufacture about 10 years ago, but I've only put about 6K miles on it. I can't believe the ECM would have gone bad already but who knows?

I feel like I'm at the point of having to throw parts at the problem to see if anything fixes it. I'd appreciate hearing from anyone who's had a similar problem.

Thanks!
Scott

 

Few initial thoughts.

Get a scanner and get a reading on the knock readings. If a code is set due to knocks, then something is causing the ECM to count knocks. Maybe bad sensor or sensor may be picking something up.

The ECM might be causing the code to occur.

Sometime after all the troubleshooting if nothing turns up you just have to try something physical or replace something.

 

I will share my experience for what it is worth, this was on my 93 which is nearly identical. First of all let me say that like you I detest replacing parts unnecessarily.
I too ran all the tests in the FSM and both knock sensors ohm checked well within specs, the voltage supply to the sensors likewise was correct and connectors looked good, pins at the ECM were in good condition.
My first attempt to correct the problem was to install new connectors at both knock sensors thinking it must be a poor connection in spike of appearance, no such luck, the code continued to set.
Since knock sensors cost less than an ECM my next try was to replace both sensors, bingo, problem solved.
I have no idea why the sensors solved the problem, as mentioned they check good according to the FSM, however I will mention one thing that I noticed.
The acceptable range of the sensors is quite wide, 3300 to 4500 ohms., my original sensors were quite different. I do not recall the exact numbers, but lets say one was 3400 and the other was 4200, resistance of the replacements were much more closely matched, only a theory but thought I would share the experience, hope it helps.

 

pcolt94: Thanks for the response. Unfortunately, I don't have a scanner. I wonder if Autozone would be able to hook a scanner up that would count knocks or identify a problem with the ECM? I guess I could also go to the dealer and bite the bullet and let them do the diagnostics.

toptechx6: Thanks also for taking the time to reply. Based on your experience, maybe I will go ahead and change out the knock sensors before considering the ECM. Maybe I'll get lucky.

Scott

 

AutoZone will not be able to help you with this. All they can do is read codes but you need real data. I'm not even sure AZ can read a OBD1 system, they usually just drag out the OBD2 stuff.

TopTech has some interesting and valid points. If I were going to change anything it would be the sensors also. Having been in commercial and military electronics for a long time, many times electronic components or items are bad or just won't work but can check good all day. That’s why my approach is after you give it your all, and troubleshoot but nothing solid comes up, you have the make your best educated guess and try something. You can end up troubleshooting forever and never get anywhere.

 

I agree with what you're saying. You guys have convinced me to replace the sensors. I'll let you know the results, but may be a few days or next weekend.

You're right about AutoZone. They only read the the codes for OBD2, so no help here.

Thanks again for the help!

 

Well, finally got a free weekend and replaced both knock sensors today. Started it up and no SES light! Sure glad I didn't have to go the next step of replacing the ECM.

Thanks again guys for the help!

Scott

 

Hello. I was reading your post in hopes that it would provide some help to the pain I am going through.

I have replaced both knock sensors on my vehicle, cleaned the mass airflow sensor and changed all my spark plugs to E3s....that @%^#$ code STILL will not go away.

I am thinking of running new wire from the sensors straight to the ECM and seeing if that does the trick. Prior to doing that, does anyone have any idea of what the issue might be?

 

There is also an ESC (Electronic Spark Control) module involved. It is between the knock sensors and the ECM. In the earlier cars it is an external module, but somewhere along the line (I think '90, but not sure on that) they put it inside the ECM. It is a piggyback PC board that sits on top of the MEMCAL.



I think even later than that it was put on the ECM PC board. Not sure about that one either. I don't know much about the later cars, just my trusty rusty '86.

 

I agree that throwing parts at a problem is not a good idea but to me it is not a bad idea as those parts are 20 years old so it ain't a bad idea.Also keep in mind that maybe they would test bad once they get warm.Electical parts are notorious for testing good when cold & when they get hot then fail.Very common.I would have told you to just replace them since they are 20 years old & may not have fixed the problem.To me,replacing all the sensors would be a good idea if they are original & being 20 years old.No one does this as its very expensive though.Glad you got it figured out

 

If you added sealant to the threads of the knock sensors, they may not get adequate grounding to the block, and you would get code 43, no signal. New sensors come with sealant already on them, no more is needed. If you originally had a bad sensor, then replaced them, adding sealant, you would get the symptoms you describe. Try taking out the sensors, cleaning them on a wire wheel, and putting them back dry to see if the code resets.

 

Thank you all for your responses. Per the schematics, the Spark unit is not inline between the knock sensor and the ECM so I am guessing it is IN the ECM. I do not know if I can change out just that one part or if I have to get the whole ECM rebuilt.

I noticed the new knock sensors already had something on the threads so I did not see the need for any sealant. They went from box to block.

The battery has been disconnected for a couple of weeks now (since I made the original post) so maybe the computer is good and clear. I have gotten under the car and the connection to the knock sensors is solid and the wires appear to be in good order.

I appreciate you replies and look forward to becoming a more active participant in these forums.

Have a great Thanksgiving.

 

I have read through this thread and I am kinda stumped. I have a 43 code I have replaced every sensor on the engine reset the computer, also my set up is a little different. The engine is a 1996, with 1992 computer and it's in a jeep. The engine has the minimum on it wiring wise to run. The issue/light came on when my engine started missing and shuddering real bad. After a road side repair on a recent jeep trip I put in some injectors I had with me and took care of 90% of the problem but the engine check light is on and the electric fan comes on right away even while the engine is cold. Could I have toasted a couple spark plugs and the sensor is picking up a faulty spark? I am really reaching cause I am running out if ideas

 

LT1Jeep, are you using OBD1 or OBD2 knock sensors? Running a 96 LT1 with a 92 ECM you will need OBD1 knock sensors. The 96 OBD2 KS's won't work.

 

When you replaced the knock sensors (there are two) did you use 96 parts or 92? The part numbers are different, your 92 ECM may be seeing a value that is out of range if you used the 96 knock sensors.

 

Good call, I did replace my knock sensor with a 96 not a 92 sensor. So with being said I can't recall ever changing the original sensor when I put the engine in with the wire harness. I honestly don't remember if when I put the harness on if I put an older one in or not. So possibly I did have an older version knock sensor in there it went bad after 15 ish years and by me replacing it with a newer one the puter is throwing a code and turning on the fan. I know I have single wire o2 sensors and those part numbers are from a 1988 camero with a 5.7 maybe I should get a knock sensor from that same year or should I go with the 1992 year to match the puter? And I only have one knock sensor. I checked the wiring and it's all away from spark plug wires etc and is sadly in the loom all the way back.

 

And thank you for all the help

 

Sorry I forgot to answer the question about OBD 1

 

Sorry finger hit send haha
I am OBD 1

 

All Lt1's have two knock sensors. If the sensor you are using is from an 88 that is not an LT1. You need to get a wiring diagram from a 92 and duplicate it on your vehicle or you will continue to have performance problems and issues with fault codes.