Powertrain Controls - ECM/PCM

DTC 55 Fuel Lean Monitor:

Fuel System Check:

CIRCUIT DESCRIPTION
The Powertrain Control Module (PCM) can identify if the vehicle fuel system is capable of supplying enough fuel during heavy acceleration (power enrichment). When a power enrichment mode of operation is requested during "Closed Loop" operation (by heavy acceleration), the PCM will provide more fuel to the engine. Under these conditions, the Oxygen Sensor (O2S) should detect a "rich" condition. If "rich" exhaust is not detected, a DTC 55 will set.

DIAGNOSTIC TROUBLE CODE (DTC) 55 WILL SET WHEN
^ O2S is in "Closed Loop."
^ O2S voltage is less than 0.3 volt.
^ Engine is in power enrichment mode.
^ Above conditions are met for 5 seconds.
^ No DTC 13.

ACTION TAKEN (PCM WILL DEFAULT TO)
The cooling fan will enable.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. When the engine is idling or at steady cruise, the O2S voltage should vary from between approximately 100 mV to 900 mV. During power enrichment mode, more fuel is needed and O2S voltage should rise above 447 mV. This step checks if the O2S is operating properly.
2. Low fuel pressure or restricted fuel flow may cause a lean condition. Further diagnosis of the fuel system can be found on CHART A-7. Related Tests, Information and Procedures

DIAGNOSTIC AIDS
A restricted fuel filter can supply enough of fuel at idle, but may not be able to supply enough fuel during heavy acceleration.

Check for:

^ Plugged injector(s).
^ Low fuel.
^ Poor or contaminated fuel.
^ Restricted fuel supply

A DTC 55 may set as a result of vehicle running out of fuel. Refer to CHART A-7 to diagnose fuel system. Related Tests, Information and Procedures