Inspection Procedure

DTC 27 Sub Heated Oxygen Sensor Circuit

DIAGNOSTIC PROCEDURE

NOTE: When other codes are output in addition to 27 at the same time, check the circuits for other codes first.

1. CHECK VOLTAGE BETWEEN TERMINAL HT2 OF ENGINE CONTROL MODULE CONNECTOR AND BODY GROUND.
(a) Connect the Check Harness A.
(b) Turn ignition switch ON.



(c) Measure voltage between terminal HT2 of engine control module connector and body ground.

Voltage: 9.0 - 14.0 volts

- If OK proceed to step 4.
- If not OK proceed to step 2.

2. CHECK RESISTANCE OF SUB HEATED OXYGEN SENSOR HEATER.
(a) Disconnect sub heated oxygen sensor connector.



(b) Measure resistance between terminals 1 and 2 of sub heated oxygen sensor connector.

Resistance @ 20°C (68°F): 11.0 - 16.0 Ohms

- If OK proceed to step 3.
- If not OK replace sub heated oxygen sensor.

3. CHECK FOR OPEN AND SHORT IN HARNESS AND CONNECTOR BETWEEN EFI MAIN RELAY AND ECM.
- If OK check and replace ECM.
- If not OK repair or replace harness or connector.

4. CHECK VOLTAGE BETWEEN TERMINAL HT2 OF ECM CONNECTOR AND BODY GROUND.
(a) Warm up engine to normal operating temperature.



(b) Measure voltage between terminal HT2 of engine control module connector and body ground, when engine is idling and racing at 3,500 rpm.

Voltage Idling: 0.0 volts
Voltage @3,500 rpm: 9.0 - 14.0 volts

- If OK replace sub heated oxygen sensor [1].
- If not OK check and replace ECM.

[1] It is probable that the oxygen sensor has deteriorated. Usually this cannot be confirmed by eye.

WIRING DIAGRAM