Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET1990CAPRICE BROUGHAM LS, 5.0 EREPAIR AND DIAGNOSISENGINE PERFORMANCESYSTEMENGINE CONTROLS - TESTS W/CODES - CARBURETEDDIAGNOSTIC TESTSCODE 41, NO DISTRIBUTOR REFERENCE SIGNAL
1990 Chevrolet Caprice Brougham LS, 5.0 E
Code 41, No Distributor Reference Signal
1990 Chevrolet Caprice Brougham LS, 5.0 ESECTION Code 41, No Distributor Reference Signal
NOTE:
Test numbers refer to test numbers on diagnostic chart.
- This tests to see if pressure sensor voltage changes with loss of vacuum supply. When vacuum supply is lost, a properly functioning sensor will change voltage by one volt or more (measured from terminal "A" to "B" at sensor and terminal No. 20 to 22 at ECM). See CODE 34 schematic for reference.
- This tests for cause of intermittent open or ground in distributor circuit. Fault could also be a pressure sensor intermittently sticking 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 pressure sensor 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. Also see Code 34 chart.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.