Powertrain Controls - ECM/PCM

Diagnostic Trouble Code (DTC) 41:

Ignition Circuit:

CIRCUIT DESCRIPTION
The distributor ignition system provides two timing inputs to the Powertrain Control Module (PCM), high resolution signal (360 pulses per crankshaft revolution) and low resolution signal (4 pulses per crankshaft revolution). The PCM uses these two reference pulses to determine individual ignition spark timing for each cylinder.

Once the PCM calculates ignition timing, the timing signal will be sent to the ignition coil module on the Ignition Control (IC) circuit. Each timing pulse received by the ignition coil module, on the IC circuit, will trigger the coil module to operate the ignition coil. Secondary ignition voltage is induced and is then sent to the distributor for distribution to each spark plug.

The IC signal voltage ranges from about 0.5 volt to 4.5 volts.

DIAGNOSTIC TROUBLE CODE (DTC) 41 WILL SET WHEN
Voltage on CKT 423 exceeds 4.6 volts and engine speed is less than 1500 RPM.

ACTION TAKEN (PCM DEFAULT)
If a DTC 41 is detected, the PCM will disable the fuel injectors to prevent flooding of the engine. DTC 41 will be stored in the PCM memory but will not turn "ON" the Malfunction Indicator Lamp (MIL).

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

1. This determines if the DTC 41 is intermittent.

2. This check determines if the IC signal from the PCM is available at the ignition coil driver. The IC circuit voltage should be between about 0.5 and 4.5 volts.

3. The remaining tests begin to check that the coil driver circuitry is OK.

4. If all wiring and connections are OK, check the ignition coil or the ignition coil voltage supply. Check coil fuse for being open.

DIAGNOSTIC AIDS
Since the coil driver gets its power from the coil, check the ignition feed circuit to the ignition coil for opens.

DTC 41 will set only during cranking.