1995 Buick Park Avenue Code P0640 Intake Air Heater Control

Hi wayne eber,

Thank you for the donation.

DTC P0640 - Invalid Diagnostic Trouble Code. This code is not found in the DTC list.

Some generic scan tool that has not been updated would generates these and other Invalid DTC codes.

I would suggest trying a different scanner to check.

P0640 is not found in DTC list. For the description of QDM 1 fault, here is an explanation and diagnostic procedures.

CODE P1640, QDM NO. 1 CIRCUIT
PCM is used to control several components as shown in wiring schematic. PCM controls these devises through use of a Quad-Driver Module (QDM). When PCM is commanding a component on, voltage potential of output circuit will be low (near zero volt). When PCM is commanding output circuit to a component off, voltage potential of circuit will be high (near battery voltage). Primary function of QDM is to supply ground for component being controlled.

Each QDM has a fault line which is monitored by PCM. Fault line signal is available on data stream for scan tool test equipment display on Tech 1. PCM will compare voltage at QDM based on accepted values of fault line. If QDM No. 1 fault detection circuit senses a voltage other than accepted value, fault line will go from a low signal on data stream to a high signal and Code P1640 will set.
Code P1640 will set when the following conditions are present.

"Â Engine is running.
"Â PCM detects an improper voltage level on a circuit connected to QDM No. 1.
"Â Brake not applied.
"Â All conditions met for 5 seconds.
"Â PCM will illuminate Malfunction Indicator Light (MIL).

NOTE: Test numbers refer to numbers on diagnostic chart.

1 . If QDM related code is stored, diagnose that code first. Repair made to related code will repair Code P1640 also.
2 . If QDM No. 1 symptoms are present, checks on Code P1640 (2 Of 2) chart should isolate cause of fault.
3 . This test will determine which circuit is out of specification.
4 . Determines if problem is circuit or component.
5 . As factory installed PCM is protected with an internal circuit breaker, it is highly unlikely
that PCM needs to be replaced.

Diagnostic Aids
Monitor voltage at each QDM terminal while moving related harness connectors, including PCM harness. If failure is induced, voltage will change. This may assist in isolating an intermittent condition. Check for bent pins at PCM and PCM connector terminals. If code reoccurs with no apparent connector problem, replace PCM.

Hope the following is ok. I am not good with such files and the site limits the size of pictures.