Code 41 - No Distributor Reference Signal

Code 41 says that there are no distributor references pulses to the ECM at a specified engine vacuum. This code could set with the key "ON," engine "Not Running" if the vacuum sensor was indicating "Engine Running" voltage with the key just "ON." With a constant open or ground in the reference signal circuit, Code 12 would be set along with 41. Use Chart 12 if 12 and 41 are set. Code 41 alone indicates the problem is intermittent. When the distributor reference line signal is lost, the engine runs full rich and with retarded (base) spark timing. The result is poor performance, poor fuel economy, and possibly rotten egg odor from the exhaust.

1. This test checks to see if vacuum sensor voltage changes with loss of vacuum supply. A good sensor will change voltage at terms. "A" to "B" by 1 volt or more.
2. This test checks for cause of an intermittent open or ground in the distributor circuit. This includes the Hall Switch if so equipped. Fault could also be a vacuum sensor that is intermittently stuck, at the same voltage output as an engine "running," when the key is only "ON." This condition will produce no reference signal. Terminals must be removed from connector to properly check them. The distributor pick-up coil should also be checked.