Code P1640, QDM "A" Error: Notes

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 "A" 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 following conditions are present.

• Engine is running.
• PCM detects an improper voltage level on a circuit connected to QDM "A".
• Above conditions met for 5 seconds.

PCM will illuminate Malfunction Indicator Light (MIL).

1. PCM does not know which controlled circuit caused Code P1640. This chart will go through each of circuits to determine which is at fault. If QDM related codes are present, use applicable code chart first.
2. QDM "A" related code will include Code P0740.
3. QDM "A" symptoms:
   • Cooling fan No. 2 on all time or will not come on at all.
   • Poor driveability due to 100 percent canister purge.
   • TCC does not engage.
4. This test will determine if problem is circuit or component. As factory installed PCM is protected with an internal circuit breaker, it is highly unlikely that PCM needs to be replaced.
5. This test will determine which circuit is out of specifications.