DTC P1605 Lost Communications with HVAC Control System. Buick Regal 1997

For 1990-2009 cars only

Makes 🢒 Buick 🢒 1997 🢒 Regal 🢒 Engine 🢒 Engine Controls - 3.8L 🢒 DTC P1605 Lost Communications with HVAC Control System

Refer to Data Line in Electrical Diagnosis.

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 Fail 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.

•	DTC can be cleared by using the scan tool Clear Info function or by disconnecting the PCM battery feed.

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.

DTC P1605 - HVAC Serial Data Circuit

Step	Action	Value(s)	Yes	No
1	Was the Powertrain On-Board Diagnostic (OBD) System Check performed?	--	Go to Step 2	Go to the Strategy Based Diagnostic Flow
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?	--	Go to Step 3	Go to Step 4
3	Turn OFF the ignition switch. Disconnect the PCM and the HVAC Controller. Check the serial data circuit for an open between the HVAC controller and the PCM. If a problem is found, repair as necessary. Refer to Repair Procedures in Electrical Diagnosis. Was a problem found?	--	Go to Step 6	Refer to Diagnostic Aids
4	Check the serial data circuit for a poor connection at the HVAC Controller. If a problem is found, repair as necessary. Refer to Repair Procedures in Electrical Diagnosis. Was a problem found?	--	Go to Step 6	Go to Step 5
5	Check the serial data circuit for a poor connection at the PCM. If a problem is found, repair as necessary. Refer to Repair Procedures in Electrical Diagnosis. Was a problem found?	--	Go to Step 6	Go to the Diagnostic Check in Heating, Ventilation and Air Conditioning
6	Review and record scan tool Fail Records data. Clear DTC(s). Operate the vehicle within Fail Records conditions. Using a scan tool, monitor Specific DTC info for DTC P1605. Does the scan tool indicate DTC P1605 failed?	--	Go to Step 2	System OK