P1635

P1635 PCM/ECM 5 Volt Reference Line Low




Circuit Description
The powertrain control module (PCM)/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 PCM/ECM monitors the voltage on the 5 volt reference. If the voltage is out of tolerance, the PCM/ECM will set DTC P1635.

Conditions for Setting the DTC
- Voltage reading is less than 4.8 V or greater than 5.2 V.
- The PCM/ECM detects a voltage out of tolerance condition on the 5 volt reference circuit.
- Every 125 milliseconds there are greater than or equal to 10 failures within 20 samplings.
- Ignition voltage is greater than 10 V.

Action Taken When the DTC Sets
- The PCM/ECM will not illuminate the Malfunction Indicator Lamp (MIL).
- The PCM/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 PCM/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 Fail 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 PCM/ECM and engine grounds for being secure and clean.

Test 1 - 6:

Test 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 PCM/ECM must be reprogrammed. Refer to the latest Techline procedure for PCM/ECM reprogramming.