DTC 26

DTC 26 Diagnostic Chart:

Oxygen Sensor Circuit:

Circuit Description:
When the 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. The PCM then uses this input to make fuel corrections to maintain the optimum air/fuel ratio.

DTC 26 will set if the following condition is met:
^ When the engine speed varies by more than 15 rpm over the preceding crank angle period during a period of 30 seconds while idling with the engine coolant temperature (ECT) above 50° C (122° F).

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

1. This checks to see if the 02S is faulty.

2. This checks for an open in the BLK wire between the PCM and 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 O2S, an open in the BRN wire to the O2S on federal emissions equipped vehicles and for a faulty PCM.

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

A rich air/fuel condition may also be caused by high fuel pressure (restricted fuel pressure regulator or return hose) faulty EVAP canister purge system a faulty MAP sensor (indicating low vacuum) or a faulty EGR system (sticking EGR valve California emissions only).

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.