Powertrain Controls - ECM/PCM

Trouble Code 41 Chart:

Ignition Wiring Schematic:

CIRCUIT DESCRIPTION
Ignition Control (IC) spark timing is provided by the Powertrain Control Module (PCM) on circuit 423. Inputs from a number of engine sensors allow the PCM to correctly calculate optimum spark timing. Engine load is calculated from the Manifold Absolute Pressure (MAP) sensor, engine RPM is derived from the 3X crankshaft position sensor, engine operating temperature from Engine Coolant Temperature (ECT) and Intake Air Temperature (IAT) sensors and engine knock activity from the knock sensor. Other engine functions modify spark to a lesser degree such as Torque Converter Clutch (TCC) engagement and Exhaust Gas Recirculation (EGR) activity. The bypass circuit controls an internal switch in the electronic Ignition Control Module (ICM). Unless the vehicle is in back-up spark (base timing mode), the bypass circuit will have 5 volts applied to it. This 5 volt signal from the PCM allows a solid state switch to direct the IC timing pulses to the ICM for sequencing and energizing the coil packs. If the bypass circuit is not energized, the IC pulses from the ICM are shunted to ground and the electronic ICM uses it's own base timing schedule to time and energize the coil packs.

DIAGNOSTIC TROUBLE CODE (DTC) 41 WILL SET WHEN
Ignition Control pulses are detected on circuit 423 when the vehicle is in bypass (no voltage applied to bypass should allow IC pulses to be grounded by the electronic ICM). The test will either pass or fail within the first 1 second of engine running. If it passes, the test will not run until the next key cycle.

ACTION TAKEN (PCM WILL DEFAULT TO)
The PCM will allow the electronic ignition control module to control timing using it's own base timing schedule. The Malfunction Indicator Lamp (MIL) will become illuminated.

DTC 41 WILL CLEAR WHEN
A current DTC 41 will clear after each ignition key cycle. A History DTC 41 will clear after 50 consecutive ignition key cycles without a current DTC 41 being stored.

TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.

1. This test confirms DTC 41 and that the fault causing the DTC is present.
2. Checks for a normal IC ground path through the IC module. An IC circuit 423 shorted to ground will also read less than 500 ohms; however, this should set a DTC 42.

DIAGNOSTIC AIDS
The scan tool does not have any ability to help diagnose a DTC 41 problem.
Refer to Computers and Controls / System Diagnosis / Procedures / Diagnosis by Symptom / Intermittents. - Intermittent Malfunctions