Powertrain Controls - ECM/PCM

DTC 55:

Chart A7: Fuel System Diagnosis:

CIRCUIT DESCRIPTION
The Powertrain Control Module's (PCM) internal circuitry can identify if the vehicle fuel system is capable of supplying adequate amounts of 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 PCM should detect a "rich" condition.

DTC 55 WILL SET WHEN:
Engine operating in "Closed Loop," not in fuel cutoff, no DTCs 44, 45, 64, 65 set. If the PCM detects lean oxygen sensor voltage for 3 seconds during power enrichment modes of operation, DTC 55 will set.

ACTION TAKEN (PCM will default to):
The Malfunction Indicator Lamp (MIL) will illuminate.

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

1. Wrap a shop towel around the fuel pressure connector to absorb any small amount of fuel leakage that may occur when installing the gage. Ignition "ON," pump pressure should be 284-325 kPa (41-47 psi). This pressure is controlled by spring pressure within the regular assembly. Pressure below 284 kPa (41 psi) may cause a lean condition and may set a DTC 44 or 64. It could also cause hard starting cold and poor driveability. Low enough pressure will cause the engine not to run at all. Restricted flow may allow the engine to run at idle, or low speeds, but may cause a surge and stall when more fuel is required, as when accelerating or driving at high speeds. Low fuel pressure under heavy acceleration conditions may set a DTC 55.
2. Restricting the fuel return line allows the fuel pressure to build above regulated pressure. With a Tech 1 (or equivalent) Scanner enable the fuel pump, pressure should rise above 325 kPa (47 psi) as the valve in the return line is partially closed.

DIAGNOSTIC AIDS
A restricted fuel filter can supply adequate amounts of fuel at idle but may not be able to supply enough fuel during heavy acceleration. A vapor lock condition can cause a DTC 55.

If a DTC 55 can not be duplicated, it may have been caused by the customer running the vehicle out of fuel.