P1635

Diagnostic Chart:

Refer to Engine Controls Schematics Fuel Controls, Engine Data Sensors: A/C Pressure, TP, MAP, ECT, IAT and IAC, EVAP Vent, Engine OIL Level and Pressure, EGR.

CIRCUIT DESCRIPTION
The PCM uses the 5 volt reference A circuit as a sensor feed to the following sensors:
^ The TP sensor
^ The MAP sensor
^ The EGR Valve pintle position sensor
^ Fuel tank pressure sensor

The PCM monitors the voltage on the 5 Volt Reference A circuit. If the voltage is out of tolerance, DTC P1635 will set.

CONDITIONS FOR SETTING THE DTC
^ The PCM detects voltage out of tolerance on the 5 Volt Reference A circuit.
^ The above condition is present for longer than 10 seconds.

ACTION TAKEN WHEN THE DTC SETS
^ The PCM will illuminate the Malfunction Indicator Lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.
^ The PCM will store conditions which were present when the DTC set as Freeze Frame and Failure Records data.
^ If the misfire is determined to be catalyst damaging, the PCM will flash the MIL.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The PCM will turn OFF the MIL during the third consecutive trip in which the diagnostic has been run and passed.
^ The History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
^ The DTC can be cleared by using a scan tool.

DIAGNOSTIC AIDS

IMPORTANT: Be sure to inspect PCM and engine grounds for being secure and clean.

Check for the following conditions:
^ Poor connection at the PCM - Inspect harness connectors for the following conditions:
- Backed out terminals
- Improper mating
- Broken locks
- Improperly formed or damaged terminals
- Poor terminal to wire connection
^ Damaged harness - Inspect the wiring harness for damage. If the harness appears to be OK, observe the MAP display on the scan tool turn ON the ignition, with the engine OFF while moving connectors and wiring harnesses related to the following sensors. A change in the MAP display will indicate the location of the malfunction.
- The TP sensor
- The FTP sensor
- The EGR valve
- The MAP sensor

If the DTC cannot be duplicated and is determined to be intermittent, reviewing the Failure Records can be useful in determining when the DTC was last set. Also refer to Testing for Intermittent and Poor Connections in Diagrams.

TEST DESCRIPTION
The number below refers to the step number on the diagnostic table.
10. This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed. Refer to PCM Replacement/Programming.