DTC 26

Code Chart 26:

Heated O2 Sensor Circuit:

CIRCUIT DESCRIPTION:

The ECM supplies a voltage of about 0.45 volt between terminals "OX+" and "OX1." (If measured with a 10 megohm digital voltmeter, this may read as low as 0.32 volt). When the O2 sensor reaches operating temperature, it varies this voltage from about 0.1 volt (exhaust is lean) to about 0.9 volt (exhaust is rich). The sensor is like an open circuit and produces no voltage when it is below 360°C (600°F).

TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.

1. Code 26 is set when the O2 sensor signal voltage on RED wire remains above 0.7 volt under the following conditions:

^ 30 seconds or more.
^ System is operating in normal operating temperature 60°C (176°F).
^ Engine run time after start is 1 minute or more.
^ Throttle angle is between 3% and 45%.

DIAGNOSTIC AIDS:

Code 26, or rich exhaust, is most likely caused by one of the following:

^ Fuel Pressure. System will go rich, if pressure is too high. The ECM can compensate for some increase. However, if it gets too high, a Code 26 will be set. Related Tests, Information and Procedures
^ Leaking injector. Related Tests, Information and Procedures
^ Canister Purge. Check for fuel saturation. If full of fuel, check canister control and hoses. Refer to COMPONENT REPLACEMENT AND REPAIR PROCEDURES in FUEL SYSTEMS.
^ MAF Sensor. An output that causes the ECM to sense a higher than normal air flow can cause the system to go rich. Disconnecting the MAF sensor will allow the ECM to set a fixed value for the MAF sensor. Substitute a different MAF sensor if the rich condition is gone, while the sensor is disconnected.
^ TPS. An intermittent Throttle Position Sensor output will cause the system to operate richly due to a false indication of the engine accelerating.
^ O2 Sensor Contamination. Inspect oxygen sensor for silicone contamination from fuel, or use of improper RTV sealant, The sensor may have a WHITE, powdery coating and result in a high but false signal voltage (rich exhaust indication). The ECM will then reduce the amount of fuel delivered to the engine causing a severe surge driveability problem.
^ EGR Valve. EGR sticking open at idle is usually accompanied by a rough idle and/or stall condition. If Code 26 is intermittent, Testing and Inspection