Status Light Indicators: ECM
The following is a brief summary of ECM system status light indicator operation.
- LOOP light (CRT equipped) or HIGH light (ECCP equipped) is on when ECM is in closed loop fuel control. Light comes on only after coolant and O2 sensors reach operating temperature.
- TCC light (CRT equipped) or MED light (ECCP equipped) only indicates whether operation is enabled or disabled by ECM. Actual working operation depends on TCC system being in working order.
- OXY light (CRT equipped) or LOW light (ECCP equipped) stays on when oxygen sensor signals rich exhaust condition to ECM. Light will flash on and off during warm engine, steady throttle, and proper fuel mix condition.
- 4th Gear light (CRT equipped) or OFF light (ECCP equipped) will be on when ECM senses 4th gear pressure switch open. Light should only be on in 4th gear.
- 3rd Gear light (CRT equipped) or AUTO light (ECCP equipped) will be on when ECM senses 3th gear pressure switch open. Light should only be on in 3rd or 4th gear.
- 2nd Gear light (CRT equipped) or "°C" light (ECCP equipped) will be on when ECM senses 2nd gear pressure switch open. Light should only be on in 2nd, 3rd or 4th gear.
- A/C Compressor Command UPPER ARROW (ECCP equipped) or COMP light CRT equipped) will be on only when ECM allows A/C clutch engagement through A/C relay. Light will also be on if BCM requests ECM to turn clutch on during test sequence. Light should be off if ECM commands disengagement.