DTC 27

DTC 27 Diagnostic Chart:

Sub-Oxygen Sensor Circuit:

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 powertrain control module (PCM) monitors this voltage and determines the concentration of gases in the exhaust after the converter. The PCM 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 PCM 0.45 volts or more and the sub-oxygen sensor input at the PCM 0.45 volts or less.

Test Description:
Numbers below refer to circled numbers on the diagnostic chart.

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

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

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

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

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 hamess connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal-to-wire connections before component replacement.