Tracker 4WD V6-2.5L VIN 4 (2001)
A degraded, or bad, TWC catalyst, 65 percent hydrocarbon conversion, will show greatly increased activity in the output voltage from the post-catalyst
heated oxygen sensor (2). The degraded catalyst post-catalyst HO2S output voltage will therefore appear similar to the typically active output voltage of
the pre-catalyst heated oxygen sensor (1).
Misfire Monitor Diagnostic Operation
The misfire monitor diagnostic is based on crankshaft rotational velocity (reference period) variations. The PCM determines the crankshaft rotational
velocity using the crankshaft position sensor and the camshaft position sensor. When a cylinder misfires the crankshaft actually slows down momentarily.
By monitoring the crankshaft and the camshaft position sensor signals, the control module can calculate when a misfire occurs.
For a non-catalyst damaging misfire, the diagnostic will be required to report a misfire that is present within 1,000 to 3,200 engine revolutions.
For a catalyst damaging misfire, the diagnostic will respond to a misfire that is within 200 engine revolutions.
Rough roads may cause a false misfire detection. A rough road will cause torque to be applied to the drive wheels and the drive train. This torque can
intermittently decrease the crankshaft rotational velocity and cause a false misfire detection.
Fuel Trim System Monitor Diagnostic Operation
The fuel system monitor diagnostic averages of short-term and long-term fuel trim values. If these fuel trim values stay at their limits for a calibrated
period of time, a malfunction is indicated. The fuel trim diagnostic compares the averages of the short-term fuel trim values and the long-term fuel trim
values to the rich and lean thresholds. If either value is within the thresholds, a pass is recorded. If both values are outside their thresholds, a rich or lean
DTC will be recorded.
In order to meet OBD II requirements, the control module uses weighted fuel trim cells in order to determine the need to set a fuel trim DTC. A fuel trim
DTC can only be set if the fuel trim counts in the weighted fuel trim cells exceed the specifications. A vehicle that has a fuel trim problem that is causing
a concern under certain conditions but operates fine under other conditions may not set a fuel trim DTC. For example an engine that is idling high due to
a small vacuum leak or an engine that is running rough due to a large vacuum leak may set an idle speed DTC or an HO2S DTC but not a fuel trim DTC.
A fuel trim DTC may be triggered by many different vehicle faults. Use all diagnostic information available when diagnosing a fuel trim fault.
