GM Trouble Codes

12 Diagnostic mode / ECM functioning No distributor pulses
13 Oxygen sensor signal problem or loss
14 Coolant sensor - high temperature fault
15 Coolant sensor - low temperature fault
16 System over voltage - over 17.1 volts
16 DIS fault
17 Crank signal circuit shorted (or bad ECM)
18 Crank signal circuit open (or bad ECM)
18 Cam/crank sensor synchronization error (DIS)
19 Fuel pump circuit shorted
19 Crankshaft position sensor fault (1988-1991)
20 Fuel pump voltage high, circuit open
21 TPS voltage high
22 TPS voltage low
23 M/C solenoid fault (Carbureted)
23 MAT sensor Low temperature fault (EFI/TPI/SFI)
23 EST bypass circuit fault (Cadillac DFI)
24 VSS loss of signal
25 MAT sensor High temperature fault (EFI/TPI/SFI)
25 Modulated displacement failure (1981 Cadillac V8-6-4)
25 EST circuit fault (Cadillac HT4100)
26 Quad driver circuit (3.8L)
26 Throttle switch circuit shorted
27 Throttle switch circuit open
27 Gear switch diagnosis
28 Gear switch diagnosis
28 PSM check (4L80-E Transmissions)
29 Gear switch diagnosis
30 ISC fault (Cadillac TBI)
30 RPM error (Cadillac MFI)
31 Turbo over-boost fault (Turbo only)
31 Park/Neutral switch fault (3.3L V-6)
31 MAT sensor circuit fault (Cadillac DFI)
31 Canister purge solenoid fault
31 Camshaft sensor circuit fault
31 EGR circuit fault (1988-1991 TBI)
31 MAP sensor circuit shorted
32 BARO sensor circuit shorted (Carbureted)
32 EGR circuit fault (EFI/TBI)
32 MAP sensor circuit open
33 MAP sensor voltage low - pressure low/vacuum high
33 MAF signal low - flow high (EFI/TPI/SFI)
34 MAP sensor voltage high - pressure high/vacuum low
34 MAF signal high - flow low (EFI/TPI/SFI)
35 ISC fault (Carbureted)
35 IAC fault (EFI/TPI/SFI)
35 BARO sensor circuit shorted (Cadillac DFI)
36 MAF sensor burn-off circuit failure
36 DIS fault
36 Transaxle shift control (1991+)
36 Closed throttle shift control (1991+)
36 BARO sensor circuit shorted (Cadillac DFI)
37 MAT sensor voltage low or shorted (Cadillac HT4100)
37 MAT sensor high temperature (1984-86)
38 MAT sensor voltage high or open (Cadillac HT4100)
38 MAT sensor low temperature (1984-86)
38 Brake input circuit failed (brake light switch)
39 TCC failure
40 Power steering pressure switch fault
41 EST circuit failure - no distributer pulses
41 Camshaft position sensor failure
41 Cylinder select error
42 EST circuit grounded (HEI module failure)
42 Front oxygen sensor lean error (Cadillac MFI)
43 ESC control failure, spark retard too long
43 TPS out of adjustment
43 Knock sensor signal
43 Front oxygen sensor rich error (Cadillac MFI)
44 Oxygen sensor lean error
45 Oxygen sensor rich error
46 Power steering pressure switch fault (4 cylinder)
46 VATS alert
46 Right/left fuel balance error (Cadillac DFI)
47 ECM failure
47 A/C clutch and Cruise Control circuit
48 Misfire diagnosis
48 EGR fault (Cadillac)
49 MAP sensor low error
51 ECM, PROM, or MEM-CAL failure
52 ECM or CALPAK failure
53 System over voltage - over 17.1 volts
53 EGR sensor fault, improper EGR vacuum (Carbureted)
53 Distributor signal fault (Cadillac HT4100)
53 VATS alert (5.0L TBI)
54 Fuel pump voltage low (below 2 volts) (EFI/TPI/SFI)
54 M/C solenoid failure (Carbureted)
55 ECM failure (poor connections or failed ECM)
55 Oxygen sensor failure
55 Fuel lean monitor error (Corvette 5.7L P)
56 Vacuum sensor circuit (Corvette Port throttle system)
56 Coolant level low
56 Quad driver B circuit (3.8L)
56 VATS alert (Cadillac)
58 PASS key fuel enable circuit
58 VATS alert
60 Transmission not in drive (Cadillac)
61 Oxygen sensor failure
61 Cruise Control vent valve solenoid fault (3.8L)
61 Secondary part throttle valve (Corvette Port throttle system)
62 Transaxle gear switch (3.1L V6, Quad 4)
62 Oil temperature sensor fault (Corvette 5.7L P)
62 Cruise Control vacuum circuit fault (3.8L)
63 MAP sensor voltage high, low vacuum/open circuit (2.8L)
63 EGR flow check (3.8L)
63 Right side oxygen sensor open error (Corvette 5.7L P)
64 MAP sensor voltage low - high vacuum/short circuit (2.8L)
64 EGR flow check (3.8L)
64 Right side oxygen sensor lean error (Corvette 5.7L P)
65 Fuel injection circuit fault (Quad 4)
65 EGR flow check (3.8L)
65 Cruise Control servo position sensor fault (3.8L)
65 Right side oxygen sensor rich error (Corvette 5.7L P)
66 A/C pressure switch low pressure (1991 +)
66 ECM fault
67 Cruise Control switch failure
67 A/C pressure switch low pressure (Chevrolet)
68 A/C relay circuit fault (Chevrolet)
68 Cruise Control system fault
69 A/C clutch circuit fault (Chevrolet)
69 A/C pressure switch high pressure
70 Intermittent TPS signal (Cadillac)
71 Intermittent MAP sensor signal (Cadillac)
72 Gear selector switch fault (Chevrolet)
73 Intermittent coolant sensor signal (Cadillac)
74 Intermittent MAT sensor signal (Cadillac)
75 Intermittent VSS signal (Cadillac)
80 TPS idle learn mode (Cadillac 4.6)
80 Fuel system rich (Cadillac)
81 Camshaft position sensor reference fault (Cadillac)
82 Camshaft position reference signal high (Cadillac)
83 *Reserved
84 *Reserved
85 Idle throttle angle too high (Cadillac)
85 TBI service required (Cadillac)
88 ECM fault (‘85 & up)
95 Engine stall detected (Cadillac)
99 Power management, Cruise Control fault (Cadillac)
107 PCM /BCM data link defect
108 PROM checksum error
109 PCM memory reset (Cadillac)
110 Generator ‘L’ terminal circuit fault (Cadillac)
112 EEPROM failure (Cadillac)
131/132 Knock sensor failure (Cadillac)

A/C Air Conditioning MAF Mass Air Flow sensor
BARO Barometric sensor (Carbureted engine MAP) MAP Manifold Absolute Pressure sensor
BCM Basic Control Module MAT Manifold Air Temperature sensor
CALPAK Calibration Package (early PROM substitute) MEM-CAL Memory Calibration module (early PROM substitute)
CTS Coolant Temperature Sensor MFI Multi-port Fuel Injection
DFI Digital Fuel Injection M/C Mixture Control servo
DIS Distributorless Ignition System PCM Programmable Control Module
ECM Electronic Engine Control Module PROM Programmable Read-Only Memory module
EEPROM Electrically-Erasable Programmable Read-Only Memory module PSM Pressure Switch Manifold
EFI Electronic Fuel Injection SFI Sequential multi-pot Fuel Injection
EGR Exhaust Gas Recirculation valve TBI Throttle Body Injection
ESC Electronic Spark Control (HEI ignition) TCC Torque Converter Clutch
EST Electronic Spark Timing control TPI Tuned-Port Induction
HEI High Energy Ignition distributor module TPS Throttle Position Sensor
IAC Idle Air Control VATS Vehicle Anti-Theft System
ISC Idle Speed Control VSS Vehicle Speed Sensor