code 42
 

this code just came on, and the car has had trouble idling some days, and other days it starts fine, but still has a code, and sometimes no code.......

i changed the ignition module, but i still have a code

any ideas? diagnostic sheets?

Re: code 42
 

First thing, how is the connector to the pick-up coil?

We have the first wire (4 way connector closest to the 2 wire connector). This is your ground through the ECM. Will see 0 volts with key on or engine running.

Second wire is the by-pass (connector needs to be disconnected to set timing). Will see 0 volts with key on and 4.75 volts with engine running.

Third wire is your reference. 0 volts with key on and 13 volts with engine running (could be 1.3 but the print-out that I have doesn't show the decimal point but has a space between 1 and 3)

Fourth is your EST. Same as reference wire.

If your by-pass line is open or grounded, the Ignition Module will not switch to EST mode so the EST voltage will be low and Code 42 will set.

Code 42 means the ECM has seen an open or short to ground in the EST or bypass circuits. This test confirms Code 42 and that the fault is causing the code is present.

Checks for normal EST ground path through the ignition module. An EST CKT 423 (white wire from ECM D4 to Ignition Module D) shorted to ground will also read less than 500 ohms; however, this will be checked later.

This is the description from what I have without going through and typing out the entire 2 pages of this diagnostic check. Let us know what you find from this and I'll see what I can dig up.

Re: code 42
 

my car is doing the same thing, i guess its back to the bike and backpack making 10:50pm runs to the auto store and walmart. they close at 11. my car died at a stop. with a code flashing. then i restarted it but when i put it into drive, it died for good. i called a tow truck, towed it and now im back to the bike. AT least i can drink and bike. haha just kidding.

Re: code 42
 

My **** did the same exact thing to me the other day!!! f-ing code 42!! i figured out it was the Bin i loaded on to my emulator. because i unplugged it and put the stock one back in and its fine. Are you guys tuning?

Re: code 42
 

Im all stock. now, except energy suspension bushings. I got it running too. it was the coil i think. I heard its best to replace the ignition module and coil at the same time, they fight each other like. TO get it going i replaced the COIL<PICKUP COIL< IGNITION MODULE. It would runn after i replaced the wires and plugs but died when hot. now after the new parts. ..its cherry,:thanks:

Re: code 42
 

well i got the code 42 diagnostic sheet for the car, i'm gonna go through the entire flow chart tonight w/ my analog multimeter and test light... i'll let you guys know what happens. thanks for the responses, especially birdtojag.... very helpful

Re: code 42
 

no success... problem comes and goes. after i drove the car w/ the check engine light the other day for about a half hour, it idled and ran ok, but it didnt have any power when i hit it.

then it sat for another half hour, when i decided to drive it again.

i start it up... no code, and best of all, when i hit it... it moved lol

whats the deal guys?

Re: code 42
 

How are the pick-up coil connections in the distributor? I've seen if those are bad, your ESC doesn't work well and feels like it won't go. Check those 2 wires under the cap and see what happens from there. Might need a new distributor.

Re: code 42
 

the distributer is new.... i think my problem might be that something is getting wet, because every time it rains, and the car is when i have the problem, but when the car is dry after it not raining for a while, it runs fine...

sounds weird, but that's what i'm experiencing.

anyone know if i could probe all the connections at the ECM to see which one is giving a weird reading? do you guys know if theres a chart out there that tells me what i should be seeing at all the different connections at the ECM????

Re: code 42
 

PM me your e-mail and I'll see what I can do about getting you one. I have one and can try to scan and send to you.

Re: code 42
 

well, it wont start anymore unless i hold down the gas. same goes for idling... it won't idle by itself.

i went though the service manual code 42 diagnostic chart, and the solution came down to my ECM being bad....

even if i change the ECM and it fixes the problem, i still want to know WHY I KEEP KILLING ECM'S

Re: code 42
 

ok guys... my code 42 mysteriously went away again today and the car seems to be runing ok except for when the car goes in to closed loop, it tends to stall and have a rough idle.

one think i think might be the culprit... the ESC (electronic spark control) module. i think this, because with the ignition on, i check the voltage at the computer harness (port B7) and its the ONLY port at the computer harness that gives less than 12v. it gives somewhere between 9.5 and 10.

is this normal to be getting this voltage at the computer harness connector???

Re: code 42
 

There is supposed to be 9.2 to 9.3 volts at that wire at the ECM. What else are you reading from the other wires?

Re: code 42
 

oh really? how did you know that???? that's exactly what i had. the other wires that have voltage, all have battery voltage (~12v) with the key on and the car off

i want to be able to probe ALL of the ECM connectors while the car is running now that i have NO check engine light... i want to make sure all of the connectors are getting proper voltages! and if i see anything funny maybe i can narrow down my problem....

my chilton manual displays all of the connections at my ECM but it doesnt display what voltages i should have while the car is runing in closed/open loop

Re: code 42
 

if its a mass car, try unplugging it. if you thinks its the ecm try the gm slap test.

Re: code 42
 

lol... the gm slap test? the car is running fine now with no check engine lights... but i know that something is wrong with it, so all i want to do is probe the ECM harness connectors with the car running to see if i can find anything that looks weird... i guess i'll try to do a few more searches on the forums for some charts displaying correct voltages at the harness connectos.... unelss my savior posts them on here lol

Re: code 42
 

light is back. i checked all the terminals at the ECM when the car was off, everything seemed to check out fine..... i'm stumped

Re: code 42
 

for any of you that actually care, it was a bad ECM..... AGAIN!!!!!!!

i've had to change the ECM in this car like 3 or 4 times in the past 6 years that i've had it because of a SES light..... drives me crazy!!!!!!!

any ideas as to why i keep killing my ECM?

Re: code 42
 

How is your connection going inside the car under the fender ? You may be getting moisture on it and shorting something out in the ECM .

Re: code 42
 

What kind of ECM are you buying? New or Reman and whose?

What did you do with the old ones? and what codes did they show?

Re: code 42
 

Go to ChevyThunder.com They have the pinouts for a 1227165 (1986-89) MAF. I have a copy but it is 3 pages long but won't paste very well (it is all columns) shows key on and engine on.

Also S-10's use the same ECM so I would be getting a backup.

Re: code 42
 

i think its a bad distributor part grounding periodically, anything that grounds the computer just straight ground, will eat your ecm. my ecm went bad when the wire leading to the dizzy had stripped insulation plastic on the wire and was between the dizzy cap and bottom dizzy. my case was a bad pickup coil (back in 06') :eek: