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Power Take-Off



DTC P0641

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Initial Inspection and Diagnostic Overview
* Review Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor
DTC P0641 00
- 5-Volt Reference Circuit

Diagnostic Fault Information





Circuit/System Description

The power take-off (PTO) is an upfitter integrated system that allows the user to create an auxiliary power source. The PTO system specifically controls engine speed to values higher than normal base idle, PTO load relay engagement, and remote starting and shutdown of the engine. When the operator requests PTO using either the PTO switch or PTO remote, the engine RPM will increase to a default standby speed. The engine control module (ECM) converts the data from the engine speed sensor to a 2 pulses/engine revolution signal. When PTO is engaged, the power take-off module (PTOM) sends a GMLAN serial data message to the ECM requesting engine speeds, in accordance with the depressed switches from the PTO switch or remote.

Conditions for Running the DTC

The engine is running.

Conditions for Setting the DTC

The PTO module detects that the 5-volt reference of the PTO switch is above or below a predetermined voltage threshold.

Action Taken When the DTC Sets

* The malfunction indicator lamp (MIL) will not illuminate.
* The PTO module records the operating conditions at the time the diagnostic fails. The PTO module stores this information in the Snapshot Records.

Conditions for Clearing the DTC

* A last test failed, or the current DTC, clears when the diagnostic runs and does not fail.
* A history DTC clears after 40 consecutive warm-up cycles, if failures are not reported by this or any other emission related diagnostic.

Diagnostic Aids

Using the Snapshot Records data may help locate an intermittent condition. If you cannot duplicate the DTC, the information in the Failure Records can help determine how many miles since the DTC set. The Fail Counter and Pass Counter can help determine how many ignition cycles that the diagnostic test reported a pass and/or a fail.

Circuit/System Verification

1. Engine ON, press 1 on the PTO switch to engage PTO. The engine RPM should increase to the default engine speed within a few seconds.
2. Disengage PTO. If equipped, use the remote switch to engage PTO. The engine RPM should increase to the default engine speed within a few seconds.

Circuit/System Testing

1. Ignition OFF. Disconnect the harness connector at the PTO switch.
2. Ignition ON, test for 4.8-5.2 volts between the 5 volt reference circuit terminal 1 and ground.

- If less than the specified range, test the 5 volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the PTO module.

- If greater than the specified range, test the 5 volt reference circuit for a short to voltage. If the circuit tests normal, replace the PTO module.

3. Verify that P0641 sets as current in the PTO module

- If the specified code does not set as current, test or replace the PTO switch.

4. Ignition OFF, connect the harness connector at the PTO switch.
5. Disconnect the harness connector at X124.
6. Ignition ON, test for 4.8-5.2 volts between the 5 volt reference circuit terminal E at the female side of the connector and ground.

- If less than the specified range, test the 5 volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the PTO module.

- If greater than the specified range, test the 5 volt reference circuit for a short to voltage. If the circuit tests normal, replace the PTO module.

7. Ignition ON, test for 0 volts between the 5 volt reference circuit terminal E at the male side of the connector and ground.

- If greater than the specified value, test the 5 volt reference circuit between X124 and the upfitted remote PTO switch assembly for a short to voltage. If the circuit tests normal, test or replace the upfitted remote PTO switch assembly.

8. Ignition OFF, test for infinite resistance between the 5 volt reference circuit terminal E at the male side of the connector and ground.

- If less than the specified value, test the 5 volt reference circuit for a short to ground. If the circuit tests normal, test or replace the upfitted remote PTO switch assembly.

9. If all circuits test normal, replace the PTO module.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure. Verification Tests

* Power Take-Off Switch Replacement
* Control Module References for PTO module replacement, setup, and programming

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