C4 - code 42 (Electronic Spark Timing Circuit (EST))
Le Mans Master
Joined: Aug 2003
Posts: 9,884
Likes: 3
From: Magnolia Mississippi
St. Jude '03-'04-'05-'06-'07
Re: C4 - code 42 (tmcorvette)
thats the connector you undo for base timing... located on main harness, usually by wiper motor... my 87 has tan wire with black stripe...
could also be stuffed in the wire bundle...
could also be stuffed in the wire bundle...
Drifting
Joined: Aug 2000
Posts: 1,251
Likes: 0
Re: C4 - code 42 (tmcorvette)
42 Electronic Spark Timing (EST) circuit - open or shorted to ground during engine run
OR Direct Ignition System (DIS) fault - bypass circuit open or shorted ground during engine run
OR Fuel Cutoff Relay Circuit - open or shorted to ground
OR Direct Ignition System (DIS) fault - bypass circuit open or shorted ground during engine run
OR Fuel Cutoff Relay Circuit - open or shorted to ground
Safety Car
Joined: Feb 2002
Posts: 4,212
Likes: 10
From: Sun City West Az
Re: C4 - code 42 (nobodyunknown)
Have you had your knock sensor(s) out recently? They need to be torqued to 14lbs. To tight and they can cause a code to trigger. Otherwise, the car is 15 yrs old and they may need replacment. They are fairly cheap. :thumbs:
Thread Starter
Advanced
Joined: Feb 2003
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From: Budapest Budapest
Re: C4 - code 42 (Damien89)
Sometimes when the engine is not cold there isn't any code, but if the car is not started for one day the code 42 appear. Did you check the knock sensor?
Safety Car
Joined: Jan 2001
Posts: 4,386
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From: Boise ID
Re: C4 - code 42 (tmcorvette)
Here's a little blurb from my 87 manual....
Circuit Description:
When the system is running on the Ignition Module, that is, no voltage on the bypass line, the Ignition Module grounds the EST signal. The ECM expects to see no voltage on the EST Line during this condition. If it sees a voltage, it sets Code 42 and will not go into the EST mode.
When the rpm for EST is reached (about 400 rpm), and bypass voltage applied, the EST should no longer be grounded in the Ignition Module so the EST voltage should be varying.
If the bypass 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 be set.
If the EST line is grounded, the Ignition Module will switch to EST, but because the line is grounded there will be no EST signal. A Code 42 will be set.
Circuit Description:
When the system is running on the Ignition Module, that is, no voltage on the bypass line, the Ignition Module grounds the EST signal. The ECM expects to see no voltage on the EST Line during this condition. If it sees a voltage, it sets Code 42 and will not go into the EST mode.
When the rpm for EST is reached (about 400 rpm), and bypass voltage applied, the EST should no longer be grounded in the Ignition Module so the EST voltage should be varying.
If the bypass 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 be set.
If the EST line is grounded, the Ignition Module will switch to EST, but because the line is grounded there will be no EST signal. A Code 42 will be set.
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Le Mans Master
Joined: Feb 2000
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From: Kempner Texas
Re: C4 - code 42 (Damien89)
When I first bought my 86 several years ago, I had the same problem and went throught all sorts of checks to determine the cause.
Finally, I borrowed an ECM from a buddy's 86, plugged it in , cleared the stored code and all was well.
My problem was in the ECM, so I bought a remanufactured one from O'Reilly's Auto Parts ($100). That solved the problem and I haven't had any trouble since.
Hope thisn helps.
Jake
Finally, I borrowed an ECM from a buddy's 86, plugged it in , cleared the stored code and all was well.
My problem was in the ECM, so I bought a remanufactured one from O'Reilly's Auto Parts ($100). That solved the problem and I haven't had any trouble since.
Hope thisn helps.
Jake
5th Gear
Joined: Jan 2018
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How in the hell is that help with any kind of problem about the electronic spark timi
5th Gear
Joined: Jan 2018
Posts: 5
Likes: 0
I would ask a question most places mechanics that are qualified don't even do the OB
Be sure the connector is plugged together. The most common cause is that the connector is not plugged in. OR the code was set while setting the timing, and the code was not cleared. Try clearing it, and see if it stays away. If it does, the "problem" is fixed.
You found a 17 year old thread to jump into. If you have current questions, or need help with your car, it would probably serve you best to start a new thread rather than append a 17 year old one.
You found a 17 year old thread to jump into. If you have current questions, or need help with your car, it would probably serve you best to start a new thread rather than append a 17 year old one.
