DTC 27

Sub-Oxygen Sensor:

Circuit Description:
When the sub-oxygen sensor (O2S) reaches operating temperature, it produces a varying voltage between 0.10 volts (exhaust is lean) and 1.0 volts (exhaust is rich). The engine control module (ECM) monitors this voltage and determines the concentration of gases in the exhaust after the converter. The ECM then uses this input along with the oxygen sensor (O2S) input to make fuel corrections to maintain the optimum air/fuel ratio.

DTC 27 will set if the following condition is met:

^ When the engine is warmed up and the engine is off idle for 2 seconds or more with the oxygen sensor input at the ECM 0.45 volts or more and the sub-oxygen sensor input at the ECM 0.45 volts or less.

Test Description:
1. This checks to see if the sub-O2S is faulty.

2. This checks for an open in the BLK wire between the ECM and sub-O2S.

3. This checks for an open in the BRN wire between the ECM and G106.

4. This checks for a short to ground in the BLK wire between the ECM and sub-O2S, an open in the BRN wire to the sub-O2S and for a faulty ECM.

Diagnostic Aids:
Make sure that G106 is clean and tight.

An intermittent may be caused by a poor connection, rubbed through wire insulation, or a wire broken inside the insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal-to-wire connections before component replacement.