Code 41 - No Distributor Reference Signal
Code 41 indicates that there are no distributor reference pulses to ECM at a specified engine vacuum. This code could set with ignition on and engine not running if the MAP or VAC sensor was faulty by indicating engine running voltage with ignition on. With a constant open or ground in reference signal circuit No. 430, Code 12 would be set along with Code 41. Use Code 12 chart if Codes 12 and 41 are set. Code 41 alone indicates problem is intermittent. When distributor reference line signal is lost, engine runs full rich with retarded (base) spark timing. The result is poor performance, poor fuel economy, and possibly rotten egg odor from exhaust.
NOTE:
Test numbers refer to test numbers on diagnostic chart.
- This test checks to see if MAP or vacuum sensor voltage changes with loss of vacuum supply. When vacuum supply is lost, a properly functioning sensor will change voltage at terminals "A" to "B" and ECM terminals No. 20 to 22, by one volt or more.
- This test checks for cause of an intermittent open or ground in distributor circuit. Fault could also be a MAP or vacuum sensor that is intermittently stuck at the same voltage output as an engine running condition, with the ignition switch only in "ON" position. 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.
- Since voltage change was less than one volt, problem is in MAP/VAC system. The ECM has seen engine running vacuum equivalent with no distributor reference signal, with ignition on and engine not running. If Code 12 is present with engine running, a distributor reference fault is indicated and Code 12 chart should be referred to first.