Code 42 Check Engine Light
Thread Starter
Intermediate
Joined: Oct 2011
Posts: 27
Likes: 6
From: Rhode Island, USA
Code 42 Check Engine Light
Hey there everyone, as you may have guessed from the title I have a code 42. I replaced the ICM this afternoon to no avail, and since the idle was a little high I adjusted the TPS.
The single EST wire by the battery is good, as I disconnected it and the engine immediately died so its getting current.
First question is, can a TPS or idle rpm speed over 600 rpms throw this code? (I feel like I read that in a comment on here before.) (Please don't just guess if you're unsure)
Second question, does anybody with a shop service manual willing to send me a picture of the code 42 flow chart? I've seen some online for late 80's Chevy trucks and I imagine they're the same but it wouldn't hurt to check, also the diagnostic ecm ports are probably labeled differently in those truck flow charts.
I plan on checking ground connections tonight or tomorrow and was hoping to get some info on here before I start tracing wires looking for a short.
I appreciate any help, and love reading posts and the associated comments on this forum.
Thanks in advance!
The single EST wire by the battery is good, as I disconnected it and the engine immediately died so its getting current.
First question is, can a TPS or idle rpm speed over 600 rpms throw this code? (I feel like I read that in a comment on here before.) (Please don't just guess if you're unsure)
Second question, does anybody with a shop service manual willing to send me a picture of the code 42 flow chart? I've seen some online for late 80's Chevy trucks and I imagine they're the same but it wouldn't hurt to check, also the diagnostic ecm ports are probably labeled differently in those truck flow charts.
I plan on checking ground connections tonight or tomorrow and was hoping to get some info on here before I start tracing wires looking for a short.
I appreciate any help, and love reading posts and the associated comments on this forum.
Thanks in advance!
Le Mans Master
Joined: Sep 2013
Posts: 6,192
Likes: 750
From: near the thumb in the mitten
EST codes are a PITA because it's mostly guessing. The reference signal from ICM to ECM drops out. ICM or ECM failure. 4 wire harness set timing connector, poor ECM grounds. Plug wires laying on ECM harnesses.
Thread Starter
Intermediate
Joined: Oct 2011
Posts: 27
Likes: 6
From: Rhode Island, USA
The one I was referring to was the tan and black weatherpack single wire connector by the wiper motor/ battery area like, directly in front of the brake booster. I disconnected it with the motor running and it immediately stalled. I'll double check tomorrow, although I remember searching for the tan and black wire when I tried, took a couple minutes to find it.
Thank you for your reply!
Thank you for your reply!
Instructor
Joined: Jul 2020
Posts: 227
Likes: 43
From: New Jersey
Hey there everyone, as you may have guessed from the title I have a code 42. I replaced the ICM this afternoon to no avail, and since the idle was a little high I adjusted the TPS.
The single EST wire by the battery is good, as I disconnected it and the engine immediately died so its getting current.
First question is, can a TPS or idle rpm speed over 600 rpms throw this code? (I feel like I read that in a comment on here before.) (Please don't just guess if you're unsure)
Second question, does anybody with a shop service manual willing to send me a picture of the code 42 flow chart? I've seen some online for late 80's Chevy trucks and I imagine they're the same but it wouldn't hurt to check, also the diagnostic ecm ports are probably labeled differently in those truck flow charts.
I plan on checking ground connections tonight or tomorrow and was hoping to get some info on here before I start tracing wires looking for a short.
I appreciate any help, and love reading posts and the associated comments on this forum.
Thanks in advance!
The single EST wire by the battery is good, as I disconnected it and the engine immediately died so its getting current.
First question is, can a TPS or idle rpm speed over 600 rpms throw this code? (I feel like I read that in a comment on here before.) (Please don't just guess if you're unsure)
Second question, does anybody with a shop service manual willing to send me a picture of the code 42 flow chart? I've seen some online for late 80's Chevy trucks and I imagine they're the same but it wouldn't hurt to check, also the diagnostic ecm ports are probably labeled differently in those truck flow charts.
I plan on checking ground connections tonight or tomorrow and was hoping to get some info on here before I start tracing wires looking for a short.
I appreciate any help, and love reading posts and the associated comments on this forum.
Thanks in advance!
Thread Starter
Intermediate
Joined: Oct 2011
Posts: 27
Likes: 6
From: Rhode Island, USA
So, first things first. You were absolutely right. The ECM memory is what I had unplugged. The EST connector had been cut from the connector by a previous owner with both ends spliced together. I have since gone through the checks from the service manual for code 42. More info below. Thank you for your help!
Thread Starter
Intermediate
Joined: Oct 2011
Posts: 27
Likes: 6
From: Rhode Island, USA
So today I went through the checks for code 42. I started with clearing the ECM by disconnecting the battery, once I fired up the car I got the code 42.
- Next I disconnected and removed the ECM to follow the next steps, I received no power from CKT 423 or Port D4 on the 32 pin connector.
-I then verified that I was receiving power from CKT 424 or Port D5 (tan and black EST wire) which seemed okay.
After some more troubleshooting I came to find out that there was no wire plugged into port D4 powering port A on the distributor terminal connector.
- First and most obvious question, this was obviously removed by somebody maybe inadvertently correct?
- Second, could I route a wire from the ECM connector and solder it to the Distributor Terminal Connector that leads to the ICM without any issues? How is this connector powered?
- Third, would there be a reason for someone to pull that wire? My conclusion is no, because it would immediately set off the code 42.
Thank you everyone for all of your help. You kindness and experience are much appreciated. Looking forward to reading any responses!
UPDATE: I may have been using the wrong wiring diagram smh
Gonna try again tomorrow before I hard wire anything.
- Next I disconnected and removed the ECM to follow the next steps, I received no power from CKT 423 or Port D4 on the 32 pin connector.
-I then verified that I was receiving power from CKT 424 or Port D5 (tan and black EST wire) which seemed okay.
After some more troubleshooting I came to find out that there was no wire plugged into port D4 powering port A on the distributor terminal connector.
- First and most obvious question, this was obviously removed by somebody maybe inadvertently correct?
- Second, could I route a wire from the ECM connector and solder it to the Distributor Terminal Connector that leads to the ICM without any issues? How is this connector powered?
- Third, would there be a reason for someone to pull that wire? My conclusion is no, because it would immediately set off the code 42.
Thank you everyone for all of your help. You kindness and experience are much appreciated. Looking forward to reading any responses!
UPDATE: I may have been using the wrong wiring diagram smh
Gonna try again tomorrow before I hard wire anything.
Last edited by Frankieallen10; Jan 6, 2022 at 06:22 PM.
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Thread Starter
Intermediate
Joined: Oct 2011
Posts: 27
Likes: 6
From: Rhode Island, USA
I ran through the diagnostics, confirmed the ECM had a fault and replaced it today. No more codes. Thank you everyone. Anyone needing assistance with Code 42 EST feel free to comment or leave a PM, I'd be happy to help.
