MALFUNCTION INDICATOR LIGHT
Note. A loose fuel cap will cause MIL to illuminate.
The ECM is equipped with a self-diagnostic system which detects system failures or abnormalities. When a malfunction that may affect vehicle emissions is detected during 2 sequential drive cycles, the ECM will illuminate the MIL on the instrument panel. (Scheme 91) A corresponding DTC will be stored in ECM memory. If a misfire is detected, MIL will illuminate and DTC will be stored in ECM immediately after fault is detected. If misfire is severe enough to cause catalytic converter damage, MIL will blink. MIL will continuously blink until danger to catalytic converter has passed. To retrieve stored DTC(s). See RETRIEVING DIAGNOSTIC TROUBLE CODES.
If battery is disconnected, all DTCs and freeze frame data will be erased from ECM. As a bulb check, MIL will also illuminate for about 5 seconds when ignition is turned on.
Scheme 91
SERVICE PRECAUTIONS
Before proceeding with diagnosis, following precautions must be observed
- Ensure vehicle has a fully charged battery and functional charging system.
- Visually inspect connectors and circuit wiring being worked on.
- DO NOT disconnect battery or ECM unless instructed to do so. Doing so will erase any DTCs stored in ECM. Turn ignition off before disconnecting battery or damage to ECM may result.
- DO NOT cause short circuits when performing electrical tests. DO NOT disconnect sensors with ignition on. Either procedure will set additional DTCs, making diagnosis of original problem more difficult.
- DO NOT use a test light in place of a voltmeter.
- When checking for spark, DO NOT hold coil wire more than 1/4" from ground. Damage to vehicle electronics and/or ECM may result.
- DO NOT spray carburetor cleaner on or near coils or plug wires. Allow enough time between checking areas for leaks for carburetor spray to dissipate.
- DO NOT prolong testing of fuel injectors. Engine may hydrostatically (liquid) lock.
- The control harness between ECM and Heated Oxygen Sensor (HO2S) has a shield grounded to chassis to prevent electromagnetic interference. If shield is damaged, the control harness must be replaced.
FREEZE FRAME DATA
Engine operating conditions are required to be captured and stored in ECM memory whenever a malfunction is detected. Data captured in this manner is called freeze frame data. Freeze frame data is similar to a single record of operating conditions. Whenever a malfunction is detected, corresponding record of operating conditions is recorded in the freeze frame buffer.
Freeze frame data can only be overwritten with data associated with a misfire or fuel trim malfunction. Misfire data takes priority over all other data because of its possible part-damaging (oxygen sensors, catalytic converters, etc.) effects. Freeze frame data will not be erased unless associated DTC is cleared from ECM memory.
AFTER-REPAIR PROCEDURE
After repair, clear DTC(s). See CLEARING DIAGNOSTIC TROUBLE CODES . Verify repairs by driving vehicle with scan tool connected to DLC and monitor for DTCs.
READINESS DRIVE CYCLE
Connect Hi-Scan Pro or generic scan tool to DLC. Perform Readiness Drive Cycle when directed to from diagnostic tests. Readiness drive cycle provides conditions for EVAP monitor to run, so that repairs for EVAP DTC(s) may be verified.
Failure Conditions (P0116)
ECM will set DTC P0116 and illuminate MIL when ECT sensor actual performance curve is more than 68°F (20°C) less than ECM model curve for 0.2 second during 2 drive cycles. ECM model curve is based on fuel delivery, ambient air temperature and engine operating time. This DTC indicates uncharacteristic engine temperature performance being read by ECT sensor or ECM.
Failure Conditions (P0117)
ECM will set DTC P0117 and illuminate MIL when sensor output indicates a temperature less than -49°F (-45°C) for 0.2 second during 2 drive cycles.
Failure Conditions (P0118)
ECM will set DTC P0118 and illuminate MIL when sensor output indicates a temperature more than 284°F (140°C) for 0.2 second during 2 drive cycles.
Failure Conditions (P0121)
ECM will set DTC P0121 and MIL will illuminate if engine load indicated by the TP sensor and Mass Air Flow (MAF) sensor are different. This code indicates that throttle position and air flow readings by TP and MAF sensor or ECM, do not result in expected engine load value.
Failure Conditions (P0122)
ECM will set DTC P0122 and MIL will illuminate if throttle angle is reported as less than 2.1 degrees for more than 0.2 second during 2 driving cycles. This code indicates an unusually low throttle position angle being read by TP sensor or ECM.
Failure Conditions (P0123)
ECM will set DTC P0123 and MIL will illuminate if throttle angle is reported as greater than 105.4 degrees for 0.2 second during 2 driving cycles. This code indicates an unusually high throttle position angle being read by TP sensor or ECM.
Failure Conditions (P0130)
After engine runs, ECM checks front HO2S once per driving cycle for 5 seconds. If during 2 driving cycles front HO2S output signal is not between zero millivolts and 380 millivolts while rear HO2S output signal is greater than 350 millivolts, ECM will set a DTC and MIL will illuminate. This DTC indicates uncharacteristic operation of front HO2S being read by the ECM.
Failure Conditions (P0136 & P0140)
After system is in closed-loop operation and engine has run for 3 minutes, ECM checks rear HO2S output signal. If during 2 driving cycles rear HO2S output signal is not between 400 millivolts and 500 millivolts, ECM will set a DTC and MIL will illuminate. This DTC indicates an uncharacteristic reading by rear HO2S or ECM after engine has been warmed and run for 3 minutes.
Failure Conditions (P0131)
After front HO2S is on for 3 minutes, ECM continuously measures front HO2S output every 0.5 second. If during 2 driving cycles front HO2S output falls below 50 millivolts for 0.5 second, ECM will set P0131 and MIL will illuminate. This DTC indicates an unusually lean air/fuel mixture being detected by front HO2S or ECM.
Failure Conditions (P0137)
After system is in closed-loop operation and engine has run for 3 minutes, ECM will monitor rear HO2S output voltage for 0.5 second. If during 2 driving cycles rear HO2S output falls below 50 millivolts, ECM will set P0137 and MIL will illuminate. This DTC indicates an extremely low voltage reading being detected by rear HO2S or ECM.
Failure Conditions (P0132)
After front HO2S has operated for 3 minutes, ECM continuously measures front HO2S output in 0.5 second intervals. If during 2 driving cycles front HO2S output exceeds 1.058 volts for 0.5 second, ECM will set P0132 and MIL will illuminate. This DTC indicates an extremely rich air fuel mixture being detected by front HO2S or ECM.
Failure Conditions (P0138)
After system is in closed-loop operation and engine has operated for 3 minutes, ECM will monitor rear HO2S output voltage for 0.5 second. If during 2 driving cycles rear HO2S output is greater than 1.058 volts, ECM will set P0138 and MIL will illuminate. This DTC indicates an extremely high voltage reading detected by rear HO2S or ECM.
Failure Conditions (P0133)
ECM will set DTC P0133 and illuminate MIL when ECM does not sense the following conditions during 2 drive cycles
- Over a period of 2 minutes, ECM must sense a fuel compensation factor greater than 85 percent or less than 95 percent
- ECM must make some correction in air/fuel ratio when engine speed is between 1600-3200 RPM, engine load range is 1.35-3.40 milliseconds, catalytic converter temperature is more than 702°F (372°C), and system is in closed loop.
This DTC indicates that once engine is warmed up, air/fuel ratio is not being properly adjusted by front HO2S or ECM.
Failure Conditions (P0134)
After engine has operated for 3 minutes, ECM will monitor HO2S output voltage. ECM will set DTC P0134 and illuminate MIL when front HO2S output voltage is not between 400-600 millivolts for 5 seconds during 2 drive cycles. This DTC indicates front HO2S is not active within expected range once the engine is at normal operating temperature.
Failure Conditions (Short-Term Fuel Trim)
ECM will set a DTC and MIL will illuminate if short-term fuel trim value goes 10-15 percent rich (for P0172) or if short-term fuel trim additive value is less than 0.4 millisecond, or 10-15 percent lean (for P0171) for 30 seconds during 2 driving cycles when following conditions are met
- ECM is in closed loop operation.
- Engine speed is below 1000 RPM.
- Engine coolant temperature is more than 158°F (70°C).
- EVAP canister purge system is not operating.
- Mass airflow is less than 7.5 grams per second (for P0172) or 5.5 grams per second (for P0171).
Failure Conditions (Long-Term Fuel Trim)
ECM will set a DTC and MIL will illuminate if long-term multiplicative value is less than 77 percent for 30 seconds (for P0171) or if long-term fuel trim value goes to 10-15 percent lean (for P0172) for 30 seconds during 2 driving cycles when following conditions are met
- Engine load exceeds 1.8 milliseconds.
- ECM is in close loop operation (for P0171).
- Engine coolant temperature is more than 158°F (70°C).
- EVAP canister purge system is not operating.
- Mass airflow is 5.5 grams per second or less.
- Engine speed is below 1000 RPM (for P0172).
Failure Conditions (P0261, P0262, P0264, P0265, P0267, P0268, P0270 & P0271)
ECM will set a DTC and illuminate the MIL if an open circuit, short to ground, or a short to power is detected in a fuel injector circuit during 2 drive cycles.
Failure Conditions (P0300)
ECM will set a DTC P0300 and illuminate the MIL if 2 misfires per 100 engine revolutions are detected during 2 drive cycles. Misfire rate is measured every 200 revolutions when the following conditions are met
- Speed change is less than 1000 RPM per second.
- Engine speed is 600-4000 RPM.
- Engine load is greater than 2 milliseconds.
- No fuel cut-off exists.
- Starter is not engaged.
- Vehicle is on a smooth road (acceleration sensor reports less than 0.3 g acceleration).
When misfire rate increases to 5-25 percent per 200 revolutions, there is a danger of catalytic converter damage and MIL will blink on and off. Catalytic converter temperature could exceed 3542°F (1950°C) if misfire rate increases sufficiently. This DTC indicates a problem with cylinder ignition being read by ECM.
System Definition
With ignition switch at ON or START position, voltage is applied to ignition coil. Ignition coil assembly consists of 2 coils. Ignition coils are located on rear of cylinder head. High tension leads go to each cylinder from ignition coil. Ignition coil fires 2 spark plugs on every power stroke (cylinder under compression and cylinder on exhaust stroke). Coil number one fires cylinders 1 and 4. Coil number 2 fires cylinders 2 and 3. ECM provides a switching circuit to ground for energizing primary ignition coils. ECM uses crankshaft position sensor signal to time energizing of coil. When a primary ignition coil is energized and de-energized, secondary coil produces a high voltage spike across attached spark plugs.
Failure Conditions (P0301-P0304)
ECM will set DTC P0301, P0302, P0303, or P0304 and illuminate the MIL if 2 misfires per 100 engine revolutions are detected during 2 drive cycles. The misfire rate is measured every 200 revolutions when the following conditions are met
- Speed change is less than 1000 RPM per second.
- Engine speed is 600-4000 RPM.
- Engine load is greater than 2.0 milliseconds.
- No fuel cut-off exists.
- Starter is not engaged.
- Vehicle is on smooth road (acceleration sensor reports less than 0.3 g acceleration).
When misfire rate increases to 5-25 percent per 200 revolutions, there is a danger of catalytic converter damage and MIL will blink on and off. Catalytic converter temperature could exceed 3542°F (1950°C) if misfire rate increases sufficiently. This DTC indicates a problem with a specific cylinder ignition being detected by ECM.
Failure Conditions (P0325)
ECM will set DTC P0325 if knock sensor output voltage drops to less than 0.65 volt during 2 drive cycles. This DTC will NOT illuminate MIL. ECM will perform a 4 second check when the following conditions are met
- Starter is not engaged.
- Engine speed is above 3000 RPM.
- Engine coolant temperature is above 104°F (40°C).
- Engine load is greater than 2.5 milliseconds.
This DTC indicates an unexpected vibration is being detected by knock sensor or ECM under normal engine operation.
Failure Conditions (P0335)
ECM will set DTC P0335 and MIL will be illuminated if CKP signal voltage is zero with starter engaged for 4 seconds or 8 crankshaft revolutions and Camshaft Position (CMP) sensor signal indicates engine rotation. ECM performs this check every time engine is started. DTC P0335 indicates that there is no CKP signal detected by CKP sensor or ECM when CMP sensor signal verifies engine rotation.
Failure Conditions (P0336)
ECM will set DTC P0336 and MIL will be illuminated immediately if CKP sensor signal does not indicate 2 missing teeth in exactly the same location on tone wheel during 2 successive engine revolutions. ECM performs this check for 5 seconds when engine is operating at more than 2000 RPM. DTC P0336 indicates a problem with crankshaft being read by CKP sensor or ECM.
Failure Conditions (P0340)
ECM will set DTC P0340 and MIL will be illuminated if, during 2 driving cycles there is more than one CMP sensor signal during 2 engine revolutions and engine speed is above 600 RPM. This DTC indicates unexpected camshaft position readings by CMP sensor or ECM when the engine is rotating.
Failure Conditions (P0420)
Catalytic converter efficiency is determined by comparing front HO2S and rear HO2S signals. ECM will set a DTC and illuminate MIL if front HO2S and rear HO2S signals are similar more than 60 percent of the time in 2 of 4 170-second monitoring periods during 2 drive cycles. ECM measures HO2S output signals when the following conditions are met
- ECM is operating in closed loop.
- Engine speed is 1800-3200 RPM.
- Catalytic converter temperature is more than 702°F (372°C).
- Fuel vapor canister purge function is more than 0.9.
- Vehicle is not shifting gears.
- Engine load is 1.4-4.5 milliseconds.
This DTC indicates that catalytic converter has been found to have a low efficiency according to the readings of front and rear HO2S.
Failure Conditions (P0444)
ECM will set DTC P0444 and illuminate MIL if an open circuit is detected in driver stage of EVAP system purge control solenoid circuit during 2 drive cycles.
Failure Conditions (P0445)
ECM will set DTC P0445 and illuminate MIL if a short circuit is detected in driver stage of EVAP system purge control solenoid circuit during 2 drive cycles.
Failure Conditions (P0506 & P0507)
ECM will set DTC P0506 and P0507, and illuminate MIL when for 15 seconds, the ISA driver circuit values and engine idle speed are not in agreement with values stored in the ECM during 2 drive cycles when the following conditions are met
- The ISA passes idle air at a rate above 4.1 grams/second for P0506 or 1.7 grams/second for P0507.
- Engine speed deviation is less than 200 RPM.
- Vehicle speed is zero.
- Engine coolant temperature is more than 167°F (75°C).
This DTC indicates the ISA and the engine do not agree with the ECM on the idle speed value.
Failure Conditions (P1307)
ECM will set DTC P1307 and illuminate MIL if acceleration sensor signal is less than 1.5 volts or more than 3.5 volts during 2 drive cycles. This DTC indicates an extremely rough or smooth road being sensed by the acceleration sensor or ECM.
Failure Conditions (P1308 & P1309)
ECM will set DTC P1308 or P1309 and illuminate MIL if acceleration sensor signal indicates an acceleration of 0.3 g or more when vehicle speed is zero during 2 drive cycles. This DTC indicates some type of bump being read by acceleration sensor or ECM when vehicle speed is zero.
Failure Conditions (P1505)
ECM will set DTC P1505 and illuminate MIL if ISA opening coil driver stage is open or shorted to ground during 2 drive cycles.
Failure Conditions (P1507)
ECM will set DTC P1507 and illuminate MIL if ISA closing coil driver stage is open or shorted to ground during 2 drive cycles.
Failure Conditions (P1506)
ECM will set DTC P1506 and illuminate MIL if ISA opening coil driver stage circuit is open or shorted to ground during 2 drive cycles.
Failure Conditions (P1508)
ECM will set DTC P1508 and illuminate MIL if ISA closing coil driver stage circuit is open or shorted to ground during 2 drive cycles.