P1635

Circuit Description
The Engine Control Module (ECM) uses the 5 volt reference circuit as a sensor feed to the Manifold Absolute Pressure (MAP) sensor, the Air Conditioning (A/C) Pressure sensor and the Exhaust Gas Recirculation (EGR) valve. The ECM monitors the voltage on the 5 volt reference. If the voltage is out of tolerance, the ECM will set Diagnostic Trouble Code (DTC) P1635.

Conditions for Setting the DTC
- The ECM detects a voltage out of tolerance condition on the 5 volt reference circuit.
- Voltage reading is less than 4.8 volts or greater than 5.2 volts.
- Ignition voltage is greater than 10 volts.

Action Taken When the DTC Sets
- The ECM will not illuminate the Malfunction Indicator Lamp (MIL).
- The ECM will store the conditions which were present when the DTC set as Freeze Frame and Fail Records data.
- A history DTC is stored.

Conditions for Clearing the MIL/DTC
- A history DTC will clear after 40 consecutive warm-up cycles without a fault.
- DTC(s) can be cleared by using the scan tool.

Diagnostic Aids
Check for the following conditions:
- Poor connection at the ECM. Inspect the harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, and 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 with the ignition ON and the engine OFF while moving connectors and wiring harnesses related to the following sensors:
- MAP
- A/C Pressure
- EGR valve

A change in the MAP display will indicate the location of the fault.

Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.

Inspect the ECM and engine grounds for being secure and clean.

Steps 1 - 6:

Steps 7 - 13:

Test Description
The number(s) below refer to step(s) on the diagnostic table.
1. The On-Board Diagnostic (OBD II) System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored on the scan tool for later reference.
5. A faulty EGR valve can leak a small amount of current from the ignition feed circuit to the 5 volt reference. If the problem does not exist with the EGR valve disconnected, replace the EGR valve.
11. The replacement ECM must be reprogrammed. Refer to the latest Techline procedure for ECM reprogramming.