Question about 1999 Chevrolet Silverado 1500

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HOW DO FIX A CODE #42 ON 1991 CHEVY TRUCK

WHERE IS THE ELECTRONIC SPARK TIMING (EST) ON A 1991 CHEVY TRUCK 5.7 LITER.

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Check to see if the brown and black strip wire is dissconnected by the fuel pump relay if not try dissconnecting the battery for a minute and see if the light comes back on.

Posted on Feb 21, 2009

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I HAVE A 92 SILVERADO WITH CODE 42 TRUCK SURGES AT VARIOUS SPEED CAN YOU HELP

Posted on Apr 25, 2009

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1997 jeep grand cherokee laredo 4.0L shows code 42


Code 42 - Electronic Spark Timing Circuit (EST)

Mar 17, 2015 | Jeep Cars & Trucks

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Got a 2000 chevy truck with a 5.7 motor it is running extremely rich and has a mis and showing a code of 1345


take to autoparts store, have them pull trouble code, have you replaced the OXYGEN sensor ? do it ! whens the last time you replaced both the AIR & FUEL filters ? do it ! find out code, its probably a sensor ! oxygen, like I mentioned . the MAP sensor could also be fauty . anything to do with air & fuel delivery !!! VACUUM lines, check them all, replace as necessary, TIGHTEN the mounting bolts to THROTTLEBODY, maybe the gasket is leaking ! put fuel injector cleaner in tank, next fill up . when you replaced distributor, did you replace the spark plugs & plug wires ? very important !!! EGRvalve, this valve gets clogged up severely choking the engine on these trucks !! pull it off, take a look, clean it or replace it ! when you set timing, did you follow the manual, some require you bypass the EST system, by unplugging its connection . (electronic spark timing). usually located @ firewall, under relay cover. replace the knock sensor ! todays fuel is BAD for your truck, you may think you have a miss, when you inturn have a "spark knock" , replace knock sensor @ engine block ! I think we covered it, balls in your court, hope I help you , its never just one thing, truck needs a maintenance day !!!!!!!!!

Mar 23, 2013 | 1996 Chevrolet C1500

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I was looking at a post and i found my problem in one of them, i have an 87 chevy s10 2.8L that starts up fine but as it warms up wants to die but it has that gm est system (electronic spark timing) that...


The EST if for timing ****** when a spark knock occurs it works with the knock sensor.This is not the problem what you are dealing with. if something is affecting the idle.The idle specs are 675 to 775.open the concealment plug and make your adjustment therecansmo_209.gif

Sep 12, 2011 | Chevrolet S 10 Cars & Trucks

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4 flahes, then 2 trouble code on a 1995 chevy suburban


it is a 42, 96 on up use a OBD-II system to read codes. older than 96 use an OBD-I system to read codes. 42 means - electronic spark timing or bypass fault. this means that BYPASS line is open or grounded,
2) EST line is open or grounded
3) PROM or CALPACK not seated properly in the ECM
4) Poor connections between ignition module and ECM
5) Poor routing of EST harness and/or poor quality ignition wires (EMI induced electrical noise)
6) Faulty or incorrect ignition module
7) Faulty ECM.

May 22, 2011 | Chevrolet Suburban 1500 Cars & Trucks

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Engine stalls driving down the road or on take off. Had code 42. electronic spark tining. E S T circiut fault. Cleared codes and installed a fuel pressure gauge. On test drive the motor, (3.1 EFI) still...


Trouble Code 42 indicates that there may be a malfunction in the Electronic Spark Timing (EST) system. During cranking, the timing is controlled by the ignition module and the ECM grounds the EST line. It expects to see no activity on this line at this time. When the ECM enters EST mode, it applies +5 volts to the BYPASS line and expects to see voltage variations on the EST line.
Reasons for the ECM to set Code 42:
1. System in BYPASS mode (i.e. EST line supposedly grounded) but activity sensed on EST line
2. System in EST mode (i.e. BYPASS line driven with +5 volts) but no activity seen on the EST line

Possible causes include:
1. BYPASS line is open or grounded
2. EST line is open or grounded
3. Poor connections between ignition module and ECM
4. Poor routing of EST harness and/or poor quality ignition wires (EMI induced electrical noise
5. Faulty or incorrect ignition module
6. Faulty ECM
7. Faulty Pick Up Coil
8. Faulty Ignition Control Module
9. Faulty Crank Sensor or the Crank Sensor magnet probe could be cracked

Jan 15, 2011 | 1991 Chevrolet Lumina

1 Answer

I have a 1992 gmc sonoma 2 wd 4.3L throtle body i am getting the service engine soon light and I checked the codes and I get number 42- Electronic spark timing bypass circuit or EST circuit is grounded...


CODE 42 Trouble Code 42 indicates that there may be a malfunction in the Electronic Spark Timing (EST) system.
During cranking, the timing is controlled by the ignition module while the ECM monitors the engine speed. When the engine speed exceeds 400 RPM, the ECM sends a BYPASS signal to the ignition module which switches the timing to ECM control. The ECM calculates what the timing should be then "tells" the ignition module via the EST circuit.
An open or ground in the EST circuit will stall the engine and set a Code 42. The engine can be re-started but it will run on ignition module timing.
The conditions for setting this code are:
  • System in BYPASS mode but the ignition module is still controlling timing
    - or -
  • Engine speed > 600 RPM with no EST pulses (ECM controlled timing) going to the ignition module for 200 msec.


Typical causes for this code include:
1) BYPASS line is open or grounded
2) EST line is open or grounded
3) PROM or CALPACK not seated properly in the ECM
4) Poor connections between ignition module and ECM
5) Poor routing of EST harness and/or poor quality ignition wires (EMI induced electrical noise)
6) Faulty or incorrect ignition module
7) Faulty ECM


Thank you for using fixya and keep us posted

Oct 10, 2010 | 1992 GMC Sonoma

1 Answer

What do the codes 34 and 42 stand for for a obd 1 scanner for gm


problem code 34 is in map sensor curcuit is to high. code 42 is electronic spark timing malfunction. for 42 replace est module in distributor, it has the est built into it. it controls the timing. code 34-- replacing map sensor should solve problem. good- luck!!

Oct 09, 2010 | Pontiac Grand Prix Cars & Trucks

3 Answers

I need a fire timing order for a chevy astro van v6


THE FIRING ORDER IS AS FOLLOWS : 1-6-5-4-3-2.
CYLINDER NUMBERS (front-to-rear) :
LEFT (driver side) 1-3-5
RIGHT (passenger side) 2-4-6

To set ignition timing, ensure that engine is at operating temperature, (190 degrees or above), bypass EST (electronic spark timing) by unplugging the single tan wire with a black stripe from the distributor. Ignition timing should be set at 0 degrees or TDC (top dead center). If not, loosen distributor hold down bolt and adjust, then retighten.

Mar 05, 2010 | 1993 Chevrolet Astro

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1991 chevrolet silverado truck engine hesitates, fuel injected. Gives me codes #42 and #44


Trouble Code 44 indicates that the O2 sensor is showing a persistently high exhaust oxygen content (lean), despite the efforts of the ECM to increase ...
Code 42 : Electronic spark timing (EST) circuit fault

Feb 17, 2009 | 1999 Chevrolet Silverado 1500

1 Answer

Still trying to figure it out


Obviously the 12 means that the system is functioning correctly Code 42 is electronic spark timing (EST) circuit grounded. Wiring issue from the harness to dist.

Sep 19, 2008 | 1992 Chevrolet K1500

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