Hombre XS Space Cab 2WD V6-4.3L (1998)
Three Way Catalyst (TWC) Oxygen Storage Capacity
The control module monitors the post catalyst H025 signal voltage in order to measure the oxygen storage capacity of the converter. A good
catalytic converter is indicated when the post-catalyst H025 signal voltage is relatively steady (2) compared to the pre-catalyst H025 signal voltage
(1).
A malfunctioning catalytic converter is indicated when the post-catalyst HO2S signal voltage is more active (2), similar to the pre-catalyst HO2S
signal voltage (1).
In addition to catalyst monitoring the post catalyst H025 has a limited role in fuel control.
Important: Do not use post-catalyst H025 voltage activity in order to determine the efficiency of the TWC converter unless directed to do so by a
diagnostic procedure.
The catalyst monitor on-board diagnostic tests can be effected by the following:
-
A slightly degraded or marginal catalyst
-
Fuel containing high amounts of the following contaminants:
-
Sulfur
-
Silica
-
Lead
-
Phosphorus
-
Exhaust system leaks may cause the following:
-
Prevent a degraded or marginal TWC converter from failing a diagnostic test.
-
Cause a normally functioning TWC converter to fail a diagnostic test.
-
Prevent the diagnostic test from running.
-
An aftermarket H02S. An aftermarket catalytic converter.
Misfire Monitor Diagnostic Tests
When the engine is running and a cylinder misfires the crankshaft slows down momentarily. The control module has the ability to detect this
change in speed by monitoring the input signals from the following sensors:
-
The Crankshaft Position (CKP) sensor
-
The Camshaft Position (CMP) sensor. When the control module is running the misfire on-board diagnostic tests and a misfire is detected the
misfire counter stores (accumulates) the position and the number of misfires. Two counters (accumulators) are assigned to each of the
cylinders. The counters are as follows:
-
The Current Misfire Counters. The current misfire counters store the number misfires that have occurred in the last 200 engine cycles. When
the control module detects a unacceptable amount of misfires stored in a current misfire counter the misfire on-board diagnostic test fails and a
misfire DTC will set.
-
The History Misfire Counters. When a misfire DTC is set, the history misfire counters store the total number of misfires that have occurred
every 200 engine cycles.
