Code 41, 1X Reference Circuit: Notes

The ignition module sends a signal to ECM once per revolution to indicate crankshaft position. The ECM uses this information to determine when to pulse injectors for cylinders No. 2 and 3. This signal can be described as a synchronization signal and is called 1X reference, because it occurs one time per revolution.

The ignition module applies 5 volts from terminal G to ECM terminal BC5 (L & N Body) or C11 (W Body) and in effect, switches this circuit to ground for a short period of time, 125 degrees before TDC of cylinders No. 2 and 3. Code 41 is set if ECM receives (8) 2X reference pulses without a 1X reference pulse. When Code 41 is present, ECM pulses injectors in the simultaneously mode.

NOTE: Test numbers refer to test numbers on diagnostic chart.

This determines if ECM recognizes a fault. If a Code 41 is not set here, problem is intermittent and could be caused by a loose connection.
This step simulates 1X signal.If circuit and ECM are okay, ECM should recognize the voltage drop as test light probe is removed. This step will only give accurate results if:
- Chart sequence is used (ignition off or ignition on).
- "Scan" tester is set to 1X reference.
- Terminal "G" is contacted using test light probe.

The ECM will only recognize up to 4 simulated 1X pulses under this test condition.

3) If ECM did not recognize simulation of 1X signal, circuit No. 969 (L and W Bodies) or No. 647 (N Body) may be open or shorted to ground or voltage. If circuit is okay, ECM is faulty.

4) Step 2 indicated 1X circuit is okay and ECM is capable of recognizing simulated 1X reference pulse. This indicates either a poor connection at ignition module terminal "G" or a faulty ignition module caused Code 41 to occur.