Circuit Description
The PCM uses the serial data circuit to communicate with various other devices and systems in the vehicle. The PCM ensures that communication remains established by monitoring the serial data circuit for state of health messages from the other devices using the circuit. If the PCM detects a loss of the state of health serial data message from the HVAC Controller, DTC P1605 will be set.
Conditions for Running the DTC
| • | The ignition is on. |
| • | System Voltage is greater than 8.2 volts. |
Conditions for Setting the DTC
The PCM is detecting a loss of serial data from the HVAC Controller for longer than 5 seconds.
Action Taken When the DTC Sets
| • | The PCM will not illuminate the malfunction indicator lamp (MIL). |
| • | The PCM will store conditions which were present when the DTC set as Failure Records data only. This information will not be stored as Freeze Frame data. |
Conditions for Clearing the MIL/DTC
| • | A History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | The DTC can be cleared by using the scan tool Clear Info function. |
Diagnostic Aids
An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check for the following conditions:
| • | Intermittent short circuit on the serial data circuit. |
| Refer to Data Link Connector (DLC) System check in Electrical Diagnosis and check all related wiring for an intermittent short to ground or short to voltage. |
| • | Poor connection. |
| Inspect the PCM and the affected control module harness and related connectors for improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. |
| • | Damaged harness. |
| Inspect the wiring harness for damage. Check for an intermittent short or open circuit in the wiring harnesses related to the affected control module, including the ignition positive voltage, battery positive voltage, ground, and serial data circuits. Refer to Troubleshooting Procedures in Electrical Diagnosis. |
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 conditions.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Strategy Based Diagnosis | |
2 |
Important: If a loss of DLC data has already been diagnosed using the DLC Diagnosis table, clear this DTC and continue diagnosis with the Powertrain OBD System Check. Attempt to select HVAC data with the scan tool. Can the HVAC data be displayed? | -- | ||
3 |
Was a problem found? | -- | Go to Diagnostic Aids | |
4 |
Was a problem found? | -- | ||
5 |
Was a problem found? | -- | Go to Functional Check | |
6 |
Does the scan tool indicate DTC P1605 failed? | -- | System OK |
