Reading Trouble Codes

The control module stores component failure information under a related trouble code which can be recalled for diagnosis and repair. Read trouble codes by counting Malfunction Indicator Light (MIL) flashes or with diagnostic scan tester connected to the Data Link Connector (DLC). The tester is faster, and capable of reading information which would require testing individual control module and sensor/solenoid connector terminals with a digital voltmeter. Some models REQUIRE a scan tester to pull trouble codes. See SCAN TESTER DATA and SCAN TESTER USAGE .

NOTE: When using a scan tester, there is a time delay between serial data updates. For instantaneous response, a digital voltmeter must be used.

If scan tester is not available, MIL flashes can be read by grounding DLC terminal with ignition on and engine off. For example, FLASH, FLASH, pause, FLASH, longer pause, indicates Code 21. The first series of flashes are the first digit of trouble code. The second series of flashes are the second digit of trouble code. Trouble codes are displayed starting with the lowest code. Each code is displayed 3 times and will continue as long as DLC is grounded.

NOTE: Trouble codes will be recorded at various operating times. Some codes require sensor or switch operation for 5 seconds and others may require longer under certain conditions. Some codes may not set in a service bay operational mode.

TROUBLE CODE IDENTIFICATION

Code	Probable Cause
12	No Engine Speed Sensor Reference Pulse
CODE 13	Open Oxygen Sensor Circuit
CODE 14	Coolant Sensor Signal Voltage Low
CODE 15	Coolant Sensor Signal Voltage High
CODE 16	VSS Buffer Fault
CODE 21	TPS Signal Voltage High
CODE 22	TPS Signal Voltage Low
CODE 24	Vehicle Speed Sensor - "C" & "K" Series
CODE 24	VSS Transmission Output Signal - A/T
CODE 28	Transmission Range Pressure Switch
CODE 32	EGR Circuit Error Backpressure EGR With Sol - "G" Series
CODE 32	EGR Circuit Error With Evrv Solenoid
CODE 32	EGR Circuit Error - "P" Series With Linear EGR
CODE 32	EGR Circuit Error - Series W/ Linear EGR
CODE 33	MAP Sensor Signal Voltage High
CODE 34	MAP Sensor Signal Voltage Low
CODE 35	Idle Speed Error
CODE 36	Idle Speed Actuator Fault - A/T
CODE 37	TCC Brake Switch On
CODE 38	TCC Brake Switch Off
CODE 39	TCC Stuck Off - 4L80-E Transmission
CODE 42	Ignition Control
CODE 43	Knock Sensor Without Spark Module (Dual Sensors)
CODE 43	Knock Sensor Without Spark Module (Single Sensor)
CODE 43	Knock Sensor With Spark Control Module
CODE 44	Lean Exhaust Indicated
CODE 45	Rich Exhaust Indication
CODE 51	PROM Error (Faulty Or Incorrect PROM)
CODE 52	Faulty Calpak
CODE 52	System Voltage High
CODE 53	System Voltage High
CODE 54	Fuel Pump Circuit
CODE 55	ECM/PCM Error
CODE 58	Transmission Fluid Temperature High
CODE 59	Transmission Fluid Temperature Low
CODE 66	3-2 Control Solenoid Ckt Fault 4L60-E Transmission
CODE 67	TCC Solenoid Circuit Check - 4L60-E Transmission
CODE 68	Overdrive Ratio Error - 4L80-E Transmission
CODE 69	Torque Converter Clutch Stuck On 4L60-E Transmission
CODE 69	Torque Converter Clutch Stuck On 4L80-E Transmission
CODE 72	VSS Circuit Loss Transmission Output Signal
CODE 73	Pressure Control Solenoid (Current Error)
CODE 74	Transmission Input Speed Error 4L80-E Transmission
CODE 75	System Voltage Low
CODE 79	Transmission Fluid Temperature High
CODE 81	Transmission 2-3 Error
CODE 82	Transmission 1-2 Error
CODE 83	TCC Solenoid Circuit Fault (4L80E)
CODE 85	Undefined Gear Ratio (4L80E)
CODE 86	Low Gear Ratio ERROR (4L80E)
CODE 87	High Gear Ratio ERROR (4L80E)

NOTE: On models not using "P" series codes, Code 12 should always exist when DLC test terminal is grounded with key on and engine off, but it may not be indicated by all makes of scan tester.