Initial Inspection and Diagnostic Overview
GENERAL DESCRIPTION
The closed loop emission control system has a self diagnostic ability. The ECM constantly monitors the signals from the various sensors, and when a signal deviates from what the ECM "knows" is the normal range, a trouble code is stored in the computer memory. When this happens, the "check engine" light, on the instrument panel, will illuminate. If the fault is a "hard failure" (a problem that is present while vehicle is being serviced) the "check engine" light will remain on while the engine is running. If the failure is intermittent, the light will turn off after a few seconds when the fault is not present, but a trouble code will be stored. If an intermittent fault has generated a stored trouble code, but does not reoccur within the next 50 engine starts, that code will be erased automatically.
In many cases, a mechanical condition may cause some sensor signals to deviate from their normal range and set codes. For this reason, it is important to make sure that all mechanical systems are in good condition and all engine adjustments are set at the factory specifications before suspecting a computer related failure.
ALDL Connector And Diagnostic Test Leads:
DISPLAYING TROUBLE CODES
The "Check Engine" light is used to warn the operator of a system failure, and to display any trouble codes that may be stored. When the ignition is turned "on", the "check engine" lamp should lite. This is a bulb check to determine that the lamp is working. When the engine is started, the lamp should turn off.
Two connectors (diagnostic leads), located near the ECM connector, are used to activate the diagnostic mode. To enter diagnostic mode, connect the two leads together with the ignition switch turned on and the engine NOT running. The ECM will display codes by flashing the "check engine" lamp. The first code to display should be a code 12. This is not a trouble code, but indicates that the self diagnostics are functioning. Code 12 is displayed by a flash, followed by a short pause, then two flashes, followed by a longer pause. If other codes are present besides code 12, they will display in the same manner after code 12 is displayed three times. For example, code 23 is displayed by two flashes at regular intervals, followed by a short pause, then three flashes at regular intervals, followed by a longer pause. Each code is displayed three times, then the next higher numerical code will be displayed. When all codes have been displayed, code 12 will be repeated. If no trouble codes are stored, code 12 will simply display repeatedly, until the diagnostic mode is exited by disconnecting the diagnostic test leads. Be sure leads are disconnected before starting engine.
Main Fuse Location:
CLEARING CODES FROM MEMORY
After displaying and recording any trouble codes, or after repairing any faults in the system, the computer memory should be cleared of all trouble codes by interrupting the power supply to the ECM for 30 seconds. This can be done by removing the #3 fuse (in the fuse box of the instrument panel) or the main fuse (in the fuse and relay block of the engine compartment) or by disconnecting the battery. Be sure the ignition is turned off when disconnecting or reconnecting power to the ECM. After clearing trouble codes, it may be necessary to reset digital clocks or radio station presets.
TROUBLE CODE IDENTIFICATION
The "CHECK ENGINE" light will only be "ON" if the malfunction exists under the conditions listed below. If the malfunction clears, the light will go out and a trouble code will be set in the ECM. Code 12 does not store in memory. If the light comes "on" intermittently, but no code is stored, see DIAGNOSIS BY SYMPTOM under TESTING PROCEDURES. Any codes stored will be erased if no problem reoccurs within 50 engine starts.
The trouble codes indicate problems as follows:
TROUBLE CODE 12 No ignition reference pulses to the ECM. This code is not stored in memory and will only flash while the fault is present. This code is displayed before the engine is started.
TROUBLE CODE 13 Oxygen sensor circuit - The engine must run 1 minute at part throttle, under road load, before this code will set. This code does not set when the coolant temperature is below 70°C (158°F) and/or the time since engine start has exceeded 2 minutes.
TROUBLE CODE 14 Shorted coolant sensor circuit - The engine must run 2 minutes before this code will set.
TROUBLE CODE 15 Open coolant sensor circuit - The engine must run 5 minutes before this code will set.
TROUBLE CODE 21 Idle switch and MAP sensor failure.
1. Vehicle speed is 0 km/h and engine speed is between 200 and 1,000 rpm. MAP sensor output voltage is more than 500 mmHg ABS as input signal for 5 seconds.
2. Idle switch is "OFF" MAP sensor output voltage is less than 100 mmHg ABS as input signal for 5 seconds.
3. MAP sensor output voltage is between 400 and 450 mmHg ABS as input signal, and engine speed is more than 1500 rpm. Idle switch is "ON" for more than 5 seconds.
If either condition 1, 2, or 3 exists, this code will set.
TROUBLE CODE 22 Fuel cut solenoid circuit open or grounded - The engine must run under the decelerating condition over 2000 engine rpm before this code will set.
TROUBLE CODE 23 Duty solenoid circuit open or grounded.
TROUBLE CODE 25 AIR VSV. circuit open or grounded.
TROUBLE CODE 26 Canister VSV. circuit open or grounded.
TROUBLE CODE 27 Constant high voltage from VSV. to ECM.
TROUBLE CODE 31 No ignition reference pulses to the ECM after 10 seconds at part throttle, under load. This code will store in memory.
TROUBLE CODE 32 EGR system failure and sensor circuit failure.
TROUBLE CODE 34 EGR gas sensor circuit failure.
TROUBLE CODE 44 Fuel metering lean
TROUBLE CODE 45 Fuel metering rich
TROUBLE CODE 51 Shorted fuel cut solenoid circuit and/or faulty ECM.
TROUBLE CODE 52 Faulty ECM - Problem is RAM in ECM.
TROUBLE CODE 53 Shorted AIR VSV. and/or faulty ECM.
TROUBLE CODE 54 Shorted vacuum control solenoid and/or faulty ECM.
TROUBLE CODE 55 Faulty ECM - Problem is A/D converter in ECM.