Diagnostic Instructions
DTC Descriptor
DTC P2536: Accessory/Wakeup Input Performance
Diagnostic Fault Information
Circuit
| Short to Ground
| Open/High Resistance
| Short to Voltage
| Signal Performance
|
Accessory Wakeup Serial Data
| U1814
| P2536, U0100, U1010
| --
| --
|
Circuit/System Description
The accessory wakeup serial data circuit is a positive voltage signal to wake up the engine control module (ECM) and the transmission control module (TCM). The signal is activated in 2 ways; any time the ignition switch is in the ACC
or RUN position, or anytime the body control module (BCM) determines that communication is needed from the powertrain. When the ignition switch is in the ACC or RUN position, the accessory voltage circuit input to the BCM is internally connected to the
accessory wakeup serial data circuit output, and voltage is supplied to the modules. The BCM also supplies voltage to the accessory wakeup serial data circuit when it determines that communication is necessary with the powertrain and the ignition is not in the
ACC or RUN position such as during remote start.
Conditions for Running the DTC
| • | The system voltage is between 9-16 volts. |
| • | The vehicle power mode master requires serial data communication to occur. |
Conditions for Setting the DTC
The TCM senses an open on the accessory wakeup serial data circuit.
Action Taken When the DTC Sets
| • | The modules use a default value for the missing parameters until the next ignition cycle. |
| • | The modules are never signaled, therefore the specific subsystems will not function. |
| • | The vehicle may not start. |
Conditions for Clearing the DTC
| • | A current DTC clears when the condition is no longer present. |
| • | A history DTC clears when the module ignition cycle counter reaches the reset threshold of 40, without a repeat of the condition. |
Diagnostic Aids
| • | Use the DMM MIN/MAX function to capture/locate intermittent conditions. |
| • | Open/High Resistance may also set multiple no communication codes for GMLAN high speed modules. |
Reference Information
Schematic Reference
Connector End View Reference
Master Electrical Component List
Electrical Information Reference
Circuit/System Testing
- Using the DTC Descriptors and Diagnostic Aids above, determine the module that is not communicating that should be tested.
- Ignition OFF, disconnect the harness connector of the module that is not communicating.
Important: Only the high speed GMLAN modules have the serial data communication enable circuit OR the accessory wakeup serial data circuit. Refer to the module schematics to identify which modules have these circuits. If the module
that is not communicating does not have one of these circuits, proceed to step 4.
- Ignition ON, verify that a test lamp illuminates between the serial data communication enable circuit or the accessory wakeup serial data circuit and ground.
| ⇒ | If the test lamp does not illuminate, repair the circuit for an open/high resistance. If the circuits test normal, replace the BCM. |
- Ignition ON, verify that a test lamp illuminates between all battery positive voltage circuits and ground.
| ⇒ | If the test lamp does not illuminate, repair the circuit for a short to ground or an open/high resistance. If the circuit fuse is open, also test the positive voltage outputs of the module for a short to ground. If the circuits test normal, replace
the faulty module. |
- Verify that a test lamp illuminates between all ignition voltage circuits and ground.
| ⇒ | If the test lamp does not illuminate, repair the circuit for a short to ground or an open/high resistance. If the circuit fuse is open, also test the positive voltage outputs of the module for a short to ground. If the circuits test normal, replace
the faulty module. |
- Test for less than 1 ohm between the module ground circuits and ground.
| ⇒ | If greater than 1 ohm, repair the ground circuit for an open. |
- Use Data Link References to determine if the non-communicating module should use low speed GMLAN serial data.
| ⇒ | If the module is GMLAN high speed only, replace the module. |
- Test for less than 1 ohm in the low speed GMLAN serial data circuit between the non-communicating module and the module that displays the DTC.
| ⇒ | If greater than 1 ohm, test the low speed GMLAN serial data circuit for open/high resistance. |
- If all circuits test normal, replace the module that is not communicating.
Repair Instructions
Perform the
Diagnostic Repair Verification
after completing the diagnostic procedure.
Control Module References
for module replacement, setup, and programming
