Powertrain Controls - ECM/PCM

Quad Driver "B" Circuit Diagram (EGR, Boost Control, And Transaxle Solenoids):

CIRCUIT DESCRIPTION
The PCM controls several components, such as those shown in the diagram, by completing the circuit to ground. The "QUAD DRIVERS" are the electronic switches that make and break circuits to turn certain components "ON" and "OFF". Each QDM has a fault line that is monitored by the PCM. When the QDM detects a voltage in a circuit other than the accepted value for that circuit in a particular state, the fault line signal will go high and a code 56 will set. For example, when the QDM grounds circuit 922, the boost solenoid is being commanded "ON", and the measured voltage in circuit 922 should go low (drop to near zero volts). If the measured voltage in the circuit, as monitored by the PCM, remains high (near battery voltage), a faulty QDM or poor PCM ground is indicated.

Code 56 will set when the following conditions exist:
^ Engine is running.
^ PCM detects a voltage value in a driven circuit that is not within the established range for that circuit in its given state (voltage high when it should be low, voltage low when it should be high).
^ Conditions are present for more than 5 seconds.

TEST DESCRIPTION

Code 56 Diagnostic Chart (1 Of 3):

Numbers below refer to circled numbers on diagnostic charts.
1. The PCM does not "know" which of the controlled circuits caused the code 56. This chart will go through each of the circuits to determine which is at fault. If QDM related codes are present (codes 36, 39, 54, 55, 57) check those codes first.
2. If QDM "B" related symptoms are present, the checks on part 3 of 3, of this diagnostic chart should isolate the problem circuit.

Code 56 Diagnostic Chart (2 Of 3):

3. This test will determine which circuit is at fault causing the code.

Code 56 Diagnostic Chart (3 Of 3):

4. This test will determine if the problem is the circuit or the component.
5. The factory installed PCM is protected by internal circuit breakers and highly unlikely to be the cause of the problem. If the PCM needs to be replaced, check all other circuits for shorts to power or ground before connecting a new PCM.