Engine Controls - Tests W/codes: Other Geo Tracker I

MALFUNCTION INDICATOR LIGHT (MIL)

Note. MIL is also known as the CHECK ENGINE light.

All vehicles are equipped with a Malfunction Indicator Light (MIL), located on instrument panel. Light comes on, as a bulb check, when ignition switch is turned to ON position and engine is not running. Light should not flash at this time and should go out when engine is started.

If MIL remains on or flashes with engine running, self-diagnostic system has detected a problem. If problem goes away, light will go out after 10 seconds, but a fault code will be stored in ECM memory.

All trouble codes except Code 41 (ignition signal circuit) are stored in ECM memory. Code 41 is erased from memory as soon as ignition is turned off. In order to detect an active Code 41, connect a scan tester to Data Link Connector (DLC). Crank engine for 3 seconds, and leave ignition switch in ON position. If ignition switch is turned to OFF position, a hard or active Code 41 will be lost.

Hard Failures

Hard failures will cause Malfunction Indicator Light (MIL) to glow and remain on until malfunction is repaired. If light comes on and remains on (light may flash) during vehicle operation, cause of malfunction must be determined using diagnostic (code) charts. If a sensor fails, ECM will use a substitute value in its calculations to continue engine operation. In this condition, vehicle is functional, but loss of good driveability will most likely occur.

Intermittent Failures

Intermittent failures may cause Malfunction Indicator Light (MIL) to flicker or glow and go out after intermittent fault goes away. However, corresponding fault code will be retained in ECM memory. If fault does not reoccur within a certain time frame, related fault code will be erased from ECM memory. Intermittent failures may be caused by sensor, connector or wiring related problems. See INTERMITTENTS in TESTS W/O CODES article in this section.

RETRIEVING CODES

1. Perform diagnostic circuit check before diagnosing vehicle using self-diagnostic system. See appropriate DIAGNOSTIC CIRCUIT CHECK chart under «DIAGNOSTIC CODE CHARTS»(ref-19477-S16694042592001010200000).
2. Fault code(s) can be retrieved using a scan tester connected to Data Link Connector (DLC) or by counting flashes of Malfunction Indicator Light (MIL) after grounding the diagnostic request terminal in the duty check data link connector, located near battery. (Scheme 45)and (Scheme 46).
3. Turn ignition off. Using a jumper wire, jumper between duty check data link connector terminals No. 2 and 3. Turn ignition on and observe MIL to read fault codes. Proceed to appropriate charts under «DIAGNOSTIC CODE CHARTS»(ref-19477-S16694042592001010200000) to diagnose fault codes.
4. If no fault codes are stored, MIL will flash Code 12, indicating ECM diagnostic system is operating. If fault codes are stored, code will flash 3 times starting with the lowest code.

Scheme 45

Scheme 46

CLEARING CODES

Turn ignition switch to OFF position. Remove TAIL/DOME fuse or remove 40-amp fusible link (Green) in underhood fuse/relay block for at least 30 seconds. ECM fault code memory is now clear. If 40-amp fusible link is removed to clear ECM memory, clock and radio memory will also be erased.

CHART A-1, NO MALFUNCTION INDICATOR LIGHT (MIL)

Malfunction Indicator Light (MIL) should remain on when ignition switch is in ON position and engine is not running. Battery voltage is applied to indicator bulb. ECM controls indicator bulb and turns it on by providing a ground path through Purple/Yellow wire to ECM.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Checks if ECM is receiving power.
2. Checks if ECM is faulty.
3. Checks for open in Blue/Black wire between main relay and ECM.
4. Checks if ECM has a good ground.
5. Checks for open in Black/White wire to instrument panel, and Purple/Yellow wire to ECM.
6. Checks if main relay switch is receiving power.
7. Checks if main relay coil is receiving power.
8. Checks if main relay or ECM is faulty, or for open in Blue wire between main relay and ECM.
9. Checks for a faulty ignition switch or open in Black/Blue or Black/White wires to IG-COIL METER fuse.

CHART A-2, WONT FLASH CODE 12 OR ANY CODES, MIL ON STEADY

Malfunction Indicator Light (MIL) will flash trouble codes when diagnostic request terminal in duty check data link connector is grounded. On vehicles with Federal emissions, MIL is also activated by a mileage switch at 50,000, 80,000 and 100,000 miles, alerting operator that vehicle is in need of regular maintenance service. Once service is performed, MIL cancel switch should be reset. Cancel switch is located behind instrument panel, attached to left speaker.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Checks for a short to ground in Purple/Yellow wire.
2. Checks for a faulty ECM or open in Blue/Yellow and Black wires to duty check data link connector.
3. Checks for short to ground in instrument panel printed circuit.
4. Checks to see if MIL cancel switch or mileage switch is faulty.

CODE 13, HEATED OXYGEN SENSOR CIRCUIT, OPEN CIRCUIT

Heated Oxygen (O2) sensor produces a voltage that varies within a range of about 0.1 volt (lean exhaust) to 1.0 volt (rich exhaust). O2 sensor has a built-in heater that keeps O2 sensor at operating temperature while engine is running. O2 sensor is like an open circuit and produces no voltage when sensor temperature is less than 600°F (316°C), causing an open loop condition.

Code 13 will set if the following conditions are met for at least 30 seconds

1. Engine operating temperature is greater than 158°F (70°C).
2. Engine running for at least 2 minutes.
3. Engine speed is greater than 260 RPM.
4. MAP sensor pressure is greater than 350 mm Hg of vacuum.
5. Heated O2 sensor temperature less than 600°F (360°C). NOTE: Test numbers refer to test numbers on diagnostic chart.

1. Checks for short to voltage in Yellow/Blue wire or a faulty ECM.
2. Checks for short to ground in Yellow/Blue wire, a faulty ECM or a faulty O2 sensor.

CODE 14, ECT SENSOR CIRCUIT, LOW TEMPERATURE INDICATED

Engine Coolant Temperature (ECT) sensor is a thermistor in series with a fixed resistor in ECM. ECM applies 5 volts to sensor. ECM monitors voltage across ECT sensor and converts it into a temperature reading. When engine is cold, ECT sensor resistance is high. When engine is warm, ECT sensor resistance is low. Therefore, when engine is cold, ECM receives a high voltage input and when engine is warm, ECM receives a low voltage input.

Code 14 will set when voltage input at ECM indicates coolant temperature less than -54°F (-48°C) for at least 5 seconds.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test simulates Code 15. If ECM stores Code 15, ECM and its wiring are okay and ECT sensor is faulty. If Code 14 resets, ECT sensor is okay and wiring to ECM or ECM is faulty.
2. This test determines whether an open exists in Red/Yellow or Gray/Yellow wires, a short to B+ exists in Red/Yellow wire or ECM is faulty.

CODE 15, ECT SENSOR CIRCUIT, HIGH TEMPERATURE INDICATED

Engine Coolant Temperature (ECT) sensor is a thermistor in series with a fixed resistor in ECM. ECM applies 5 volts to sensor. ECM monitors voltage across ECT sensor and converts it into a temperature reading. When engine is cold, ECT sensor resistance is high. When engine is warm, ECT sensor resistance is low. Therefore, when engine is cold, ECM receives a high voltage input and when engine is warm, ECM receives a low voltage input.

Code 15 will set when voltage input at ECM indicates coolant temperature greater than 284°F (140°C) for at least 5 seconds.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test simulates Code 14. If ECM stores Code 14, ECM and its wiring are okay and ECT sensor is faulty. If Code 15 resets, ECT sensor is okay and wiring to ECM or ECM is faulty.

CODE 21, TP SENSOR CIRCUIT, SIGNAL VOLTAGE HIGH

Throttle Position (TP) sensor consists of a potentiometer that changes resistance with throttle valve position. ECM provides a 5-volt reference voltage to TP sensor. ECM reads voltage across TP sensor and converts voltage into throttle position. When TP sensor resistance decreases, throttle valve opening increases to Wide Open Throttle (WOT) and voltage monitored by ECM increases. When TP sensor resistance increases, throttle valve opening decreases to idle and voltage monitored by ECM decreases.

Code 21 will set when high voltage input at ECM is indicated with engine running at idle for at least 5 seconds.

Note. Test numbers refer to test numbers on diagnostic chart.

1. With TP sensor disconnected, voltage input at ECM should go low if ECM and its wiring are okay. If voltage input remains high, short to voltage is present in Gray wire or ECM is faulty.

CODE 22, TP SENSOR CIRCUIT, SIGNAL VOLTAGE LOW

Throttle Position (TP) sensor consists of a potentiometer that changes resistance with throttle valve position. ECM provides a 5-volt reference voltage to TP sensor. ECM reads voltage across TP sensor and converts voltage into throttle position. When TP sensor resistance decreases, throttle valve opening increases to Wide Open Throttle (WOT) and voltage monitored by ECM increases. When TP sensor resistance increases, throttle valve opening decreases to idle and voltage monitored by ECM decreases.

Code 22 will set when low voltage input at ECM is indicated with engine running at idle for at least 5 seconds.

Note. Test numbers refer to test numbers on diagnostic chart.

1. By connecting a jumper between TP sensor cavities, voltage input at ECM should be high, indicating a faulty TP sensor. If voltage input is low, problem is in ECM or ECM wiring.
2. Checks for open or short to ground in Gray and Gray/Red wires, and a faulty ECM.

CODE 23, IAT SENSOR CIRCUIT, LOW TEMPERATURE INDICATED

Intake Air Temperature (IAT) sensor is a thermistor in series with a fixed resistor in ECM. ECM applies 5 volts to sensor. ECM monitors voltage across IAT sensor and converts it into a temperature reading. When outside temperature is cold, IAT sensor resistance is high. When outside temperature is warm, IAT sensor resistance is low. Therefore, when outside temperature is cold, ECM receives a high voltage input and when outside temperature is warm, ECM receives a low voltage input.

Code 23 will set when voltage input at ECM indicates air temperature less than -52°F (-47°C) for at least 5 seconds.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test simulates Code 25. If ECM stores Code 25, ECM and its wiring are okay, and IAT sensor is faulty. If Code 23 resets, IAT sensor is okay, and wiring to ECM or ECM is faulty.
2. Checks for open in Red/Black or Gray/Yellow wires, a short to B+ in Red/Black wire or a faulty ECM.

CODE 24, VEHICLE SPEED SENSOR (VSS) CIRCUIT

ECM provides 5 volts to Vehicle Speed Sensor (VSS). While vehicle is moving, a reed switch inside VSS will open and close, toggling voltage signal high and low. ECM then converts this toggled high/low voltage into vehicle speed that is displayed as MPH/KPH.

Code 24 will set if a constant voltage signal (high or low) is not detected at ECM for at least 4 seconds, with engine running and vehicle moving.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Checks if problem is intermittent.
2. If VSS is not receiving 5 volts from ECM, Code 24 will set. Checks for open or short to B+ in Yellow wire, or a faulty ECM.
3. Checks for a poor ground connection, an open in Black/Yellow wire or a faulty VSS.

CODE 25, IAT SENSOR CIRCUIT, HIGH TEMPERATURE INDICATED

Intake Air Temperature (IAT) sensor is a thermistor in series with a fixed resistor in ECM. ECM applies 5 volts to sensor. ECM monitors voltage across IAT sensor and converts it into a temperature reading. When outside temperature is cold, IAT sensor resistance is high. When outside temperature is warm, IAT sensor resistance is low. Therefore, when outside temperature is cold, ECM receives a high voltage input and when outside temperature is warm, ECM receives a low voltage input.

Code 25 will set when voltage input at ECM indicates air temperature greater than 284°F (140°C) for at least 5 seconds.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test simulates Code 23. If ECM stores Code 23, ECM and its wiring are okay, and IAT sensor is faulty. If Code 25 resets, IAT sensor is okay, and wiring to ECM or ECM is faulty.

CODE 31, MAP SENSOR CIRCUIT, HIGH VOLTAGE INPUT - HIGH VACUUM

MAP sensor responds to changes in manifold pressure (vacuum). ECM applies 5 volts to MAP sensor. Changes in pressure, engine load and RPM are converted into voltage input monitored by ECM. A low voltage reading at ECM indicates low manifold pressure and a high voltage at ECM indicates high manifold pressure.

Code 31 will set when high voltage input at ECM indicates intake manifold pressure greater than 840 mm Hg of vacuum for at least second.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Checks for open or short to voltage in Gray/Green wire and a faulty ECM. Under normal conditions Gray/Green wire should carry a little less than 5 volts. A short to 5 volts or B+ will cause Code 31 to set.
2. Checks for open in Gray/Yellow wire, poor connection at MAP sensor or ECM, and a faulty MAP sensor or ECM.

CODE 32, MAP SENSOR CIRCUIT, LOW VOLTAGE INPUT - LOW VACUUM

MAP sensor responds to changes in manifold pressure (vacuum). ECM applies 5 volts to MAP sensor. Changes in pressure, engine load and RPM are converted into voltage input monitored by ECM. A low voltage reading at ECM indicates low manifold pressure and a high voltage at ECM indicates high manifold pressure.

Code 32 will set when low voltage input at ECM indicates intake manifold pressure less than 40 mm Hg of vacuum for at least .2 second.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Checks if ECM is providing a 5 volt reference.
2. Checks for bias voltage to MAP sensor which has a value between 4.5 and 4.9 volts.

CODE 41, IGNITION SIGNAL CIRCUIT, NO SIGNAL (1 OF 2)

ECM receives an ignition signal when ignition switch is turned to ON position. When ignition switch is turned to START position, this signal is toggled on and off through ignitor. As this signal is toggled on and off, so is ignition coil, thus inducing a voltage in secondary coil of ignition coil. Induced voltage is used to fire spark plugs.

Code 41 will set when toggled ignition signal is not present at ECM within 3 seconds of cranking. NOTE: Test numbers refer to test numbers on diagnostic chart.

Note. Step numbers refer to steps located on flow charts.

1. Checks for power to ignition coil.
2. Checks for a poor connection or a faulty ignition coil.
3. Checks for open in Brown/White wire to noise suppressor filter.
4. Checks for a poor connection or a faulty noise suppressor filter.
5. Checks for open in Brown wire to ECM.
6. Checks for open in Brown/White to ignitor.
7. Checks ignitor for good ground.
8. Checks if ECM is toggling ignition signals. Either an open, a short to ground, or a faulty ECM or ignitor.

CODE 42, CAMSHAFT POSITION SENS CKT, NO SIGNAL FOR 2 SECONDS

When distributor shaft rotates, a fluctuating magnetic field is generated due to changes in air gap between Camshaft Position (CMP) sensor and distributor shaft signal rotor. As a result, a reference voltage is induced in CMP sensor. This reference voltage is monitored by ECM to determine the crank angle input. ECM uses crank angle input to determine when to ground igniter, controlling ignition coil and ignition timing.

Code 42 will set when crank angle input is not present at ECM for 2seconds.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Checks if problem is in CMP sensor and its wiring, or faulty ECM.
2. Checks for open in White wire.
3. Checks for open in Blue/Black wire.
4. Checks for poor ground connection and open Black/Green wire, or misadjusted or faulty CMP sensor.

CODE 44, IDLE SWITCH CIRCUIT, OPEN CIRCUIT OR MISADJUSTED

Throttle Position (TP) sensor has an idle switch that sends a signal to ECM. ECM applies 5 volts to idle switch. Idle switch is closed with engine at idle (low voltage signal at ECM) and open with engine off idle (high voltage signal at ECM). When ECM detects a low voltage signal, throttle valve is closed and when ECM detects a high voltage signal, throttle valve is open.

Code 44 will set when high voltage input at ECM is indicated with engine running at idle (less than 1000 RPM) for at least 10 seconds.

Note. Test numbers refer to test numbers on diagnostic chart.

1. By jumpering TP sensor, ECM should detect a low voltage signal and Tech 1 should indicate ON. This determines whether problem is inwiring, ECM, or a misadjusted or faulty TP sensor.
2. Checks for open in Gray/Yellow and Blue/White wires, and a faulty ECM.

CODE 45, IDLE SWITCH CIRCUIT, CIRCUIT GROUNDED OR MISADJUSTED

Throttle Position (TP) sensor has an idle switch that sends a signal to ECM. ECM applies 5 volts to idle switch. Idle switch is closed with engine at idle (low voltage signal at ECM) and open with engine off idle (high voltage signal at ECM). When ECM detects a low voltage signal, throttle valve is closed and when ECM detects a high voltage signal, throttle valve is open.

Code 45 will set when low voltage input at ECM is indicated with engine running off idle (greater than 2900 RPM), and MAP sensor reading is greater than 320 mm Hg of vacuum, for at least 5 seconds.

Note. Test numbers refer to test numbers on diagnostic chart.

1. By disconnecting TP sensor, ECM should detect a high voltage signal and Tech 1 should indicate OFF. Checks for short to ground in Blue/White wire.
2. Checks for short to B+ in Gray/Red wire, or a misadjusted or faulty TP sensor.

CODE 51, EGR CIRCUIT (CALIF. ONLY)

Exhaust Gas Recirculation (EGR) temperature sensor is mounted on top of EGR valve. EGR temperature sensor is a variable resistor that changes along with temperature of exhaust gases. ECM applies 5 volts to EGR temperature sensor and reads voltage across sensor. As exhaust gas temperature increases, sensor resistance decreases providing ECM with a low voltage input. When exhaust gas temperature decreases, sensor resistance increases providing ECM with a high voltage input. ECM calculates exhaust gas temperature by voltage inputs received.

Code 51 will set when one of the 2 following conditions are met

1. EGR temperature sensor is shorted with engine coolant temperature less than 104°F (40°C) and exhaust gas temperature is greater than 428°F (220°C) for at least 3 seconds.
2. EGR temperature sensor is open with engine coolant temperature greater than 158°F (70°C) and intake air temperature is greater than 122°F (50°C) for at least 80 seconds. NOTE: Test numbers refer to test numbers on diagnostic chart.

1. Checks for proper EGR valve operation.
2. Checks for 5-volt reference to EGR temperature sensor.
3. Checks for short to voltage in Red/Green wire.
4. Checks for open Gray/Yellow wire, a faulty ECM or EGR temperature sensor.

CODE 53, GROUND CIRCUIT, CIRCUIT OPEN (CALIF. ONLY)

On California vehicles, an additional ground is supplied to ECM. ECM supplies 5 volts to Black/Green wire through a fixed resistor. ECM expects voltage signal to be low. Code 53 will set when a high voltage signal is indicated at ECM for 3 seconds.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Probing Black/Green wire cavity with test light to B+, checks for open in Black/Green wire, a poor ground connection or a faulty ECM.

SUMMARY

If no hard fault codes are present, driveability symptoms exist or intermittent codes exist, proceed to TESTS W/O CODES article in this section for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.