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Home >> Geo >> 1991 >> Prizm Base, 4D Hatchback, Standard >> Repair and Diagnosis >> Engine Performance >> Testing & Diagnosis >> Engine Controls - Tests W/Codes >> PRIZM EXCEPT GSi CODE CHARTS (VIN 6) >> Code 51, No A/C Signal

Code 51, No A/C Signal

The A/C amplifier supplies a signal to the ECM when A/C is selected. This signal allows the ECM to adjust engine speed to compensate for additional load on engine. Code 51 will set if this signal is not present.

NOTE: Test numbers refer to test numbers on diagnostic chart.
  1. Determines if a signal is being sent from A/C switch.
  2. Determines if A/C amplifier is sending a signal to A/C clutch relay.
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