Powertrain Controls - ECM/PCM

EGR Control Circuit:

Code 54 and 55 are EGR flow test failures. The PCM tests the medium and large EGR solenoid valves by cycling each of them "ON" momentarily while monitoring engine speed. When a solenoid is turned "ON", the PCM expects to see a drop in engine rpm. If the expected drop does not occur, code 54 or 55 is set. For the medium flow solenoid, if there is no change in engine speed in 6 of 8 tests, code 54 is set. If the large flow EGR solenoid fails 3 of 5 tests, a code 55 is set.

The PCM will run the EGR flow tests when the following conditions exist.
^ Coolant temperature greater than 71°C (160°F)
^ Vehicle in "coast down" condition (but not in fuel cut-off mode).
^ Oxygen sensor signal voltage greater than 0.60 volt.
^ Vehicle in 1st or 2nd gear.
^ Engine speed between 800 - 1,200 rpm (medium flow EGR solenoid check.)
^ Engine speed between 900 - 1,400 rpm (large flow EGR solenoid check.)

TEST DESCRIPTION

Codes 54 & 55 Diagnostic Chart:

Numbers below refer to circled numbers on diagnostic chart.
1. You should notice a change in engine speed when each solenoid is cycled "ON" and "OFF" again. Solenoid #3 may cause the engine to stumble and die when cycled "ON" with the engine idling.
2. If the test lamp lights, the PCM and wiring are OK.

NOTE: If the EGR valve shows signs of excessive heat, check the exhaust system for restriction (possibly a plugged catalytic converter.) Refer to EMISSION CONTROL DEVICES and see CATALYTIC CONVERTER under TESTING AND INSPECTION PROCEDURES. If the exhaust system is restricted, repair the cause of the restriction first. Check for:
^ Excessive rich condition caused by leaking injector(s); grounded injector driver circuit; faulty PCM; excessive fuel pressure; oxygen sensor circuit false lean indication (exhaust manifold leak).

DIAGNOSTIC AIDS
An intermittent condition may be caused by a poor connection, worn through wire insulation, or a wire broken inside the insulation. Check for:
^ Poor connection or damaged wiring harness. Inspect connectors for backed out terminals, improper mating, broken connector locks, improperly formed, bent or damaged terminal connectors, poor wire to terminal connection (terminal crimped onto insulation), etc.
^ If connections and harness check out OK, the fault may be intermittent. Connect a digital voltmeter to the suspect circuit(s) and monitor voltage while pulling/wiggling the wiring harness and connectors. If the fault is induced while monitoring the faulty circuit, a change in the voltage reading should occur, indicating the fault is in that circuit.