Trouble code 42 question


It costs money to go fast
Aug 1, 2001
I have two error codes stored in the computer. 13 which is the O2 and 42 which is Electronic spark timing failure. Read the explanation on GNTTYPE.ORG but still am not sure what I need to check or fix or how to check it.

Can anybody help?
Assuming that you do not have a translator (if so it could be the wiring) or direct scan (if so it could be the connection) the code 42 has a good chance of being the module - at least it was for me. I would look for a known good module/coil pack to try.
From TurboLink files....HTH

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


Trouble Code 13 indicates that the exhaust stream oxygen content sensor (O2 sensor) is not responding as expected. When cold, the sensor is 'biased' by the ECM to about 450 millivolts. Before it warms to at least 600 deg F (315 deg C) it acts as an open circuit and when the ECM reads it, it reads the 450 mV bias. The ECM expects the sensor to warm in a short period of time and begin sending its own voltages.

The conditions for setting this code are:

engine running at least 40 seconds and
no code 21 or 22 (TPS errors) present, and
coolant temperature is at least 118 deg F (48 deg C), and
O2 sensor voltage not fluctuating (i.e. steady between 350 and 557 mV), and
TPS signal indicates above idle (over 6%), and
all the above conditions met for more than 8 seconds

Typical causes for this code include:

1) Defective or degraded O2 sensor
2) Deposit contaminated O2 sensor (running leaded fuel, RTV silicone deposits etc.)
3) Corroded/defective O2 sensor connection
4) Defective sensor ground circuit
5) Defective connection at ECM
6) Defective ECM