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Code 41, 1X Reference Circuit: Notes

The ignition module sends a signal to the 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" through circuit No. 969 to ECM terminal "BC5" 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 with no 1X reference pulses. When Code 41 is present, ECM pulses injectors in the simultaneously mode.

NOTE: Test numbers refer to test numbers on diagnostic chart.
  1. This determines if ECM recognizes a fault. If a Code 41 is not set at this point, problem is intermittent and could be the result of a loose connection.
  2. This step simulates 1X signal. ECM should recognize the drop in voltage as test light probe is removed, if circuit and ECM are okay. This step will also give accurate results only if chart sequence is used (ignition off or ignition on), "Scan" tester set to 1X reference and terminal "G" contacted using test light probe.
  3. If ECM did not recognize simulation of 1X signal, circuit No. 969 may be open or shorted to ground or voltage. If circuit No. 969 is okay, ECM is faulty.
  4. Step 2 indicated that circuit No. 969 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.
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