ECM Codes 32 and 42?

[arlbrl]

Can someone tell me what the codes 32 and 42 mean and what needs to be done to correct the issues?  They are from a 1990 Suburban with a 350 EFI in a 1985 C10.  Thanks in advance.

Edited by: roundedline at: 3/1/07 5:38 pm

[VileZambonie]

CIRCUIT DESCRIPTION
The ECM operates a solenoid to control the Exhaust Gas Recirculation (EGR) valve. This solenoid is normally closed. By providing a ground path, the ECM energizes the solenoid which then allows vacuum to pass to the EGR valve.

The ECM monitors EGR effectiveness by de-energizing the EGR control solenoid thereby shutting off vacuum to the EGR valve diaphragm. With the EGR valve closed and O2 sensor fluctuating normally, fuel integrator counts will be greater than they were during normal EGR operation. If the change is not within the calibrated window, a Code 32 will be set.

The ECM will check EGR operation when:


Vehicle speed is above 50 mph.
Engine vacuum is between 15 and 55 kPa.
No change in throttle position while test is being run.
TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart:



By grounding the diagnostic terminal, the EGR solenoid should be energized and allow vacuum to be applied to the EGR valve and the vacuum should hold.
The "Service Engine Soon" light should also flash while the diagnostic terminal is grounded. If the light does not flash, this may indicate that the quad-driver has been damaged by low resistance in the TCC circuit.
When the diagnostic terminal is ungrounded, the vacuum to the EGR valve should bleed off through a vent in the solenoid and the valve should close. The gage may or may not bleed off but this does not indicate a problem.
This test will determine if the electrical control part of the system is at fault or if the connector or solenoid is at fault.
This system uses a negative back pressure valve which should hold vacuum with engine "OFF".
When engine is started, exhaust back pressure should cause vacuum to bleed off and valve should fully close.
DIAGNOSTIC AIDS
Before replacing ECM, use an ohmmeter and check the resistance of each ECM controlled relay and solenoid coil. For example TCC, etc., refer to Chart C-9A ECM QDR Check Procedure. See ECM wiring diagrams for coil term I.D. of solenoid(s) and relay(s) to be checked. Replace any solenoid where resistance measures less than 20 ohms.

[VileZambonie]

CODE 42 - ELECTRONIC SPARK TIMING (EST)



Circuit Description :

When the system is running on the Ignition Module, that is, no voltage on the by-pass line, the Ignition Module grounds the EST signal. The ECM expects to see no voltage on the EST line during this condition. If is 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 by-pass voltage applied, the EST should no longer be grounded in the ignition module so the EST voltage should be varying.

If the 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 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.

Code 42 sets if there is an open or a short to ground in the EST or by-pass circuit.



Test Description : Numbers below refer to circled numbers on the diagnostic chart.

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 causing the code is present.
Checks for a normal EST ground path through the ignition module. An EST CKT 423 shorted to ground will also read less than 500 ohms; however, this will be checked later.
As the test light voltage touches CKT 424, the module should switch causing the ohmmeter to "overrange" if the meter is in the 100-200 ohm position. Selecting the 10-20,000 ohms position will indicate above 5000 ohms. The important thing is that the module "switched".
The module did not switch and this step checks for:
EST CKT 423 shorted to ground.
Bypass CKT 424 open.
Faulty ignition module connection or module.
Confirms that Code 42 is a faulty ECM and not an intermittent in CKTs 423 or 424.
Diagnostic Aids :

The "Scan" tool does not have any ability to help diagnose a Code 42 problem. See Diagnosis By Symptoms - No Trouble Codes Stored.

Edited by: VileZambonie  at: 2/25/07 8:58 am

[arlbrl]

Thanks for the info!!

[VileZambonie]

No problem - Good luck with it