PFI Chart A-13: Left O2 Sensor Diagnosis: Description
The ECM provides a .45 volt reference signal to the oxygen sensor on CKT 412. When warm, a properly operating oxygen sensor will drive the .45 volt reference lower (below .45 volts) to indicate a lean mixture, and higher (above .45 volts) to indicate a rich mixture. The oxygen sensor signal voltage will toggle from rich to lean rapidly, at least one toggle every two seconds, if the ECM is in good control of the air/fuel mixture. PFI Chart A-13 is designed to be used after the oxygen sensor circuit and ECM operation have been verified through the PFI SYSTEM CHECK and PFI CHART A-7: LEFT O2 SENSOR NOT READY . Chart A-13 should identify oxygen sensors that are:
- Open
Not able to drive the .45 volt reference signal high (rich) or low (lean). - Shorted
Sensor output is fixed high (above .45 volts) or low (below .45 volts) due to contaminants or internal sensor faults.
NOTE:
The following step numbers refer to circled numbers on diagnostic chart. See Fig 1
. For circuit identification, see Figure
.
- With the engine running warm (coolant temperature 85°C or greater) and at fast idle, observe engine data parameter ED32.
- While running the engine at a fast idle, observe the "Open/Closed Loop" status light, the "Auto" annunciator on the CCDIC. If the ECM switches the system to closed loop operation, then the oxygen sensor is OK. If the ECM remains in open loop operation, the coolant temperature ED04 is above 85°C, and the ECM and harness have previously been verified by PFI CHART A-7: LEFT O2 SENSOR NOT READY , then replace the oxygen sensor.
- If the voltage remains between .30 and .60 for a minimum of 1 minute, then check for the possibility of leaded or contaminated fuel (i.e. filler neck or, catalytic converter has been tampered with) before checking for a faulty oxygen sensor connection or a faulty oxygen sensor. Leaded fuel can damage the catalytic converter and oxygen sensor.
- If there is no voltage variation and if the ECM and harness are operating properly as previously verified by PFI CHART A-7: LEFT O2 SENSOR NOT READY , then check for a faulty oxygen sensor.