Powertrain Controls - ECM/PCM

DTC 48 Chart:

EGR System Circuit:

CIRCUIT DESCRIPTION
The PCM tests the exhaust gas recirculation valve by overriding the commanded position of the pintle,commanding it from the open to the closed position. The PCM then monitors rear short term fuel trim and expects to see an increase in the fuel trim valve; if the expected increase is not seen, the PCM will store DTC 48 and illuminate the Malfunction Indicator Lamp (MIL) (Service Engine Soon).
The PCM will run the EGR test when the following condition are met:

- No current DTCs 13, 17, 42, 43, 44 and 45 set.
- No history or current DTCs 14, 15, 21, 22, 24, 31, 32, 34, or 75 set.
- Vehicle has been operating in "Closed Loop" for at least 9.2 minutes.
- Engine coolant temperature is between 80°C (176°F) and 110°C (230°F).
- Manifold Absolute Pressure (MAP) is between 50.2 kPa and 80 kPa.
- Engine speed is between 1250 RPM and 1850 RPM.
- Vehicle speed is 35 mph or greater.
- Rear short term fuel trim less than 135 counts.
- EGR value commanded to maximum open position.
- System voltage greater than 11 volts.
- All above conditions present for at least 5 seconds.

DTC 48 WILL SET WHEN
- Rear short term fuel trim value increases less than 14 counts when EGR test is completed.
- Above condition during 4 key cycles.

ACTION TAKEN (PCM WILL DEFAULT TO)
DTC 48 set, the PCM will illuminate the Malfunction Indicator Lamp (MIL) (Service Engine Soon) and disable the EGR system.

DTC 48 WILL CLEAR WHEN
The fault no longer exists and the ignition switch is cycled "OFF" and "ON."

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

1. Ensures that the EGR valve is allowing EGR flow and the PCM is capable of controlling the EGR valve.
2. Ensures that CKT 435 is not shorted to ground.
3. Ensures that CKT 435 or 441 is not open and that the PCM is not a fault.

DIAGNOSTIC AIDS
An intermittent may be caused by a wire broken inside the insulation.
Check for:

Poor connection or damaged harness
Inspect PCM harness connectors for backed out terminal "A4", improper mating, broken locks, improperly formed or damaged terminal, poor terminal to wire connection and damaged harness.

Intermittent test
If connections and harness check OK, monitor a digital voltmeter connected between terminal "A4" and ground while moving related connectors and wiring harness. If the failure is induced, the voltage reading will change.

If above items are OK - Replace EGR valve.

NOTE: If the EGR valve shows signs of excessive heat, check the exhaust system for blockage (possibly a plugged converter) using the procedure found on CHART B-1. B Charts If the exhaust system is restricted, repair the cause; one of which might be an injector which is open due to one of the following:
a. Stuck.
b. Grounded driver circuit.
c. Possible faulty PCM.
If this condition is found, the oil should be checked for possible fuel contamination.