For 1990-2009 cars

The 5-volt reference circuit provides reference voltage to the exhaust gas recirculation (EGR) valve position sensor, fuel tank pressure sensor, manifold absolute pressure (MAP) sensor and throttle position (TP) sensor. The current for each 5-volt reference circuit flows through the sensor to ground, which is provided internal to the powertrain control module (PCM). The PCM regulates the 5-volt reference voltage to 5 volts under all normal operating conditions. This is necessary for accurate sensor information. The PCM monitors the 5-volt reference circuit for low and high voltage faults. DTC P1635 sets when the 5-volt reference circuit is outside a calibrated voltage range.

### DTC Parameters

DTC P1635 will set if the 5-volt reference circuit is less than 4.66 volts or greater than 5.26 volts, except PCM service P/N 21024985 or 21024986, when:

• | The condition exists from longer than 0.5 seconds.

• | The ignition is ON.

DTC P1635 diagnostic runs continuously with ignition ON.

DTC P1635 is a type A DTC.

### Diagnostic Aids

The scan tool parameter values for the TP sensor, MAP sensor, EGR sensor and fuel tank pressure sensor may only shift slightly if a short to ground or voltage on the 5-volt reference circuit occurs. ECT (engine coolant temperature), intake air temperature (IAT), FUEL LEVEL, and IGNITION 1 voltage parameters on the scan tool may NOT appear normal if DTC P1635 is active.

To locate an intermittent problem, use the scan tool to monitor DTC P1635 LAST TEST with ignition ON, engine OFF. The scan tool will display FAILED if a short on the 5-volt reference circuit exists.

DTCs P0562, P0563 and P0711 may set if a short to ground exists on the 5-volt reference circuit.

DTCs P0561, P0562 and P0711 may set if a short to direct battery voltage exists on the 5-volt reference circuit.

Important: A short to B+ on the 5-volt reference circuit will NOT set DTC P1635, PCM service P/N 21024985 or 21024986.

Driveability conditions will exist if a short on the 5-volt reference circuit is present.