VUE AWD V6-3.5L VIN 4 (2004)
A degraded 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 powertrain control module 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 1000-3200 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.
On automatic transaxle equipped vehicles, the torque converter clutch (TCC) will be disabled whenever a misfire is detected. Disabling the TCC
isolates the engine from the rest of the drive line and minimizes the effect of the drive wheel inputs (torque) on the crankshaft rotation.
When the TCC has been disabled as a result of a misfire detection, the TCC will be re-enabled after approximately 3200 engine revolutions with no
misfire is detected. The TCC will remain disabled whenever a misfire is detected. This allows the misfire diagnostic to evaluate the system.
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 the fuel trim 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 the
acceptable 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 of the diagnostic information available when diagnosing a fuel trim fault.