HARD FAILURES
Hard failures cause Malfunction Indicator Light (MIL) on instrument panel to illuminate and remain on until problem is repaired. If light comes on and remains on (light may flash) during vehicle operation, corresponding trouble code will be retained in Electronic Control Module (ECM) memory on some trouble code applications. Not all trouble codes are retained in ECM memory. The cause of malfunction must be determined using trouble code charts. If a sensor fails, Electronic Control Module (ECM) will use a substitute value in its calculations to continue engine operation. In this condition, commonly known as limp-in mode, the vehicle runs but driveability will not be optimum.
Note. The MIL may also be referred to as the CHECK ENGINE light. The MIL may not illuminate when certain failure such as faulty starter signal or A/C switch signal exists, or if certain trouble codes are set.
INTERMITTENT FAILURES
Intermittent failures may cause Malfunction Indicator Light (MIL) to flicker or illuminate and go out after intermittent fault goes away. However, the corresponding trouble code will be retained in ECM memory on some trouble code applications. Not all trouble codes are retained in ECM memory. Intermittent failures may be caused by a sensor, connector or wiring related problem. See INTERMITTENTS in TESTS W/O CODES article.
Note. Test Mode (if equipped) and Normal Mode on self-diagnostic system are used for retrieving trouble code from ECM memory. For information on different mode usage, see RETRIEVING TROUBLE CODES.
Toyota Scan Tester
Connect scan tester to appropriate Data Link Connector (DLC). see scheme 1 DLC No. 1 is used on all models. Using scan tester manufacturer's instructions, retrieve trouble codes.
Normal Mode
- Before retrieving trouble code(s), verify MIL on instrument panel comes on with ignition on and engine off. The MIL should go off when engine is started.
- If MIL does not come on with ignition on and engine off, check bulb circuit on instrument panel and wiring circuit between MIL and ECM. See appropriate wiring diagram in «WIRING DIAGRAMS»(ref-21370) article. See «ECM LOCATION»(ref-21371-S35182086342001010300000).
- If MIL remains on, self-diagnostic system has detected a malfunction or abnormality. Ensure battery voltage is greater than 11 volts and charging system is okay. Warm engine to normal operating temperature.
- Apply parking brake. Shift the transmission/transaxle into Neutral (M/T) or Park (A/T). Turn A/C and all accessories off. Ensure throttle is in idle position.
- Turn ignition on with engine off. Install Jumper Wire (SST 09843-18020) between terminals TE1 and E1 in appropriate Data Link Connector (DLC). see scheme 1
- Count number of flashes from MIL on instrument panel. If system is operating properly (with no trouble codes), MIL will flash continuously and evenly. see scheme 2
- If MIL will not flash, check TE1 and E1 wiring circuit. See appropriate TE1 & TE2 DIAGNOSTIC CIRCUIT CHECK chart under TROUBLE CODE CHARTS. See «ECM LOCATION»(ref-21371-S35182086342001010300000).
- If trouble code exists, digits of trouble code will be flashed at approximately 1/2-second intervals. A 1 1/2-second pause separates first and second digits of code. see scheme 2
- If more than one trouble code is stored, a 2 1/2-second pause will occur before next trouble code is flashed. Once all trouble codes are displayed, a 4 1/2-second pause will occur then trouble code(s) will be repeated.
- Trouble codes are displayed in order of smallest to largest. After trouble codes are retrieved, remove jumper wire to exit Normal Mode. See «NOTES ON TROUBLE CODES»(ref-21371-S30338337882001010300000). For additional information on trouble codes, see «TROUBLE CODE DIAGNOSTIC HINTS»(ref-21371-S03944057812001010300000) table under SELF-DIAGNOSTIC SYSTEM and appropriate «TROUBLE CODE IDENTIFICATION»(ref-21371-S32275598852001010300000) table under TROUBLE CODE IDENTIFICATION.
Note. To repair failure causing trouble code, refer to proper trouble code chart under TROUBLE CODE CHARTS. Once repairs for trouble code are made, trouble code must be cleared from ECM memory. See CLEARING TROUBLE CODES.
ECM POWER SOURCE CIRCUIT CHECK
When ignition switch is turned on, battery positive voltage is applied to ignition coil, closing contacts in EFI main relay and supplying power to terminals +B and +B1 of ECM.
Scheme 113
Scheme 114
Scheme 115
Scheme 116
ECM BACK-UP POWER SOURCE CIRCUIT
Battery positive voltage is supplied to BATT terminal of ECM even when ignition switch is turned off for use by the diagnostic trouble code memory, air/fuel ratio adaptive control value memory, etc.
Scheme 117
Scheme 118
SUMMARY
If no hard trouble codes are present, driveability symptoms exist or intermittent trouble codes exist, proceed to steps in TESTS W/O CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent procedures.