Equus 3123 - GM Code Reader (1982 - 1995) - Manual (Page 17)

Retrieving ECM Codes
GM 2-8
CODE SERVICE CODE DEFINITION
24 Vehicle speed sensor (VSS) - open or short circuit
problems or park/neutral switch circuit problem
25 Manifold air temperature (MAT) sensor - signal voltage
is low or high
Vacuum switching valve circuit open or shorted to
ground
ATS sensor - signal voltage is high or low
26 Quad-Driver module or Quad-driver No. 1 error
27 2nd gear switch problem
Quad-Driver module or Quad-driver No. 2 error
28 3rd gear switch
Quad-Driver module or Quad-driver No. 3 error
(Corvette)
(Transmission) Fluid pressure switch assembly - open or
short circuit problems
29 4th gear switch
Quad-Driver module or Quad-driver No. 3 error
Secondary air injection system - circuit problems
31 Manifold absolute pressure (MAP) sensor - signal
voltage is low
Fuel injector
Park/Neutral switch - circuit problems
CAM sensor - circuit problems
Engine speed control governor malfunction (Van)
Turbocharger wastegate overboost
Wastegate electrical signal - open or shorted to ground
Purge solenoid voltage high (carburetor engines)
32 Barometric pressure (BARO) sensor circuit failure
Exhaust gas recirculation (EGR) valve diagnostic switch -
closed during engine start-up or open when EGR flow
requested by ECM
Electronic vacuum regulator valve (EVRV) error (EVRV
controls EGR vacuum)