Hummer H2. Manual - part 42

The engine must be running in Closed Loop.

Engine coolant temperature above 170°F for more than 1 minute.

The PCM attempts a Purge Free Updated every other time the Cell is entered.

The engine must remain in the Cell for 20 seconds to complete a Purge Free Update.

The Purge Free Cell will update once the Purge Duty Cycle returns from 0% to some other value, and the
PCM begins Stage I of the Purge Flow Monitor.

Stage I: If any of the Purge Normal Cells are richer than their Purge Free Cell Mirrors by the calibrated
amount, Stage I Passes. Stop testing this trip. Stage I Pass Specifications. If less than the specification, continue
with Stage II.

Stage II: Perform the following:

Delay for 1 second from Stage I.

Minimum BARO more than 21.70".

Maximum Throttle Change (TPS) less than .060 volts.

Maximum MAP vacuum change less than 0.50" vacuum.

Maximum RPM change less than 96 RPM.

Maximum charging system voltage change less than 0.99 volts.

Maximum generator duty cycle change less than 14% duty cycle.

The PCM updates the Cell with purge on for 1 second. The PCM updates the Cell with purge off for 2 seconds.
In Stage II, the PCM subtracts the Purge Normal Cell value from the Purge Free Cell Value. If the difference is
greater than calibrated amount, Stage II Passes and no further testing is performed that trip.

If the difference is less than the calibrated amount, continue testing. The PCM averages the Short Term
Adaptive Memory percent and the RPM for 3 seconds. The PCM stores the averaged Short Term Adaptive
Memory and the RPM value and then reads and stores the IAC Steps. The PCM begins increasing the Purge
Flow (by increasing the Purge Solenoid Duty Cycle) .40% every 44 milliseconds. The PCM begins a new
averaging for Short Term Adaptive Memory and RPM. The PCM continues taking new IAC step readings. The
PCM compares Short Term Adaptive, RPM and IAC Steps from before the Purge Duty Cycle was increased
during Stage II until 1 of 3 things happen:

Short Term Adaptive % changes by 5.0%.

IAC Steps change by 1 Step.

RPM changes by approximately: 100 RPM

If any of the above happen, Stage II passes. If not and 99% Purge Solenoid Duty Cycle is reached, Stage II
Fails. This will cause the Purge Flow Monitor to Fail 1 Trip and Freeze Frame Data will be stored.

Secondary Air Monitor

Stage I runs when the Secondary Air Solenoid is on (Upstream Air Added). The Secondary Air Solenoid is

1998 Chevrolet Pickup C1500

DRIVE CYCLES OBD-II Vehicles - OBD-II Readiness Monitors

switched on, or goes from blocked to upstream air under the following conditions:

Secondary Air Solenoid on Times:

A. Engine Running.

B. Coolant Temp after Start-Up below 120°F ECT = 2:00 minimum, above 120°F ECT = 0:20

minimum.

In Decel and all following items met:

A. Engine Temp above 0°F.

B. Engine Temp below 154°F.

C. MAP above 19" vacuum.

D. RPM above 1220 RPM.

E. RPM below 3500 RPM.

The PCM begins Stage I: The PCM monitors the Downstream O2S while the Secondary Air Solenoid is on (in
the Upstream mode). If Downstream O2S is below .725 volts, the PCM goes to Step A. If Downstream O2S is
above .745 volts, the PCM goes to Step B.

A. If the Downstream O2S is less than .725 volts, the PCM waits for the Secondary Air to be turned off. After
the Secondary Air is turned off, the PCM monitors the Downstream O2S for 2 Seconds. If the Downstream O2S
voltage is now above .745 volts, Stage I Passes and all testing is stopped this trip. If it is not above .745 volts,
Stage I fails and Stage II begins.

B. If the Downstream O2S is greater than .745 volts with the Secondary Air Solenoid on (Upstream Air Mode),
then the PCM fails Stage I and Stage II begins. The PCM begins Stage II after the following:

Stage I Failed.

Fuel System in Closed Loop.

At Idle.

Test not already failed this Trip.

RPM above 700 RPM.

In Stage II, the PCM richens the mixture until the Downstream O2S switches rich by doing the following:

The PCM changes the Upstream O2S rich switch point from .490 volts to 1.02 volts.

The PCM increments a counter by 0.02 volts every 2 seconds.

The PCM stops updating Long Term Adaptive Memory.

The PCM turns off the purge solenoid (No Purge Flow).

The PCM uses the Purge Free Idle Cell value for fuel calculations.

The PCM modifies the Fuel Ramps of Short Term Adaptive Memory.

1998 Chevrolet Pickup C1500

DRIVE CYCLES OBD-II Vehicles - OBD-II Readiness Monitors

If the Downstream O2S does not switch to rich (above .745 volts) before the Upstream O2S counter gets to 1.12
volts, the PCM fails Stage II and the Secondary Air Monitor fails 1 trip and Freeze Frame Data is stored.

If the Downstream O2S switches to rich (above .745 volts) before the Upstream O2S counter gets to 1.196
volts, the PCM turns the Secondary Air Solenoid on (Upstream Air Mode). The PCM resets Short Term
Adaptive Memory to -1.5% and begins reducing the Short Term Adaptive Memory by -0.39% every 0.430
seconds until the Upstream O2S is below .859 volts.

Once the Upstream O2S is below .859 volts, the PCM holds the Short term Adaptive Memory at its present
value. The PCM checks to see if the Downstream O2S has switched below .725 volts. If so, the PCM Passes
Stage II and no further Testing is done this Trip. If the Downstream O2S has not switched below .725 volts,
wait a maximum of 20 Seconds. If either 20 Seconds passes or the Downstream O2S has not switched
below .725 volts, the PCM fails Stage II and the Secondary Air Monitor fails 1 trip and Freeze Frame Data is
stored.

Oxygen Sensor Heater Monitor (Both Upstream & Downstream O2)

Perform the following:

Engine running at least 5 minutes.

Shut the Engine off.

Minimum battery voltage with engine off is more than 10 volts.

The PCM delays for 5 seconds.

The PCM keeps the power to the O2S Heaters off (keeps the ASD Relay off for now).

The PCM begins pulsing the O2 Sensors with 5 volts for 35 milliseconds every 1.6 Seconds.

The PCM then monitors the O2S voltage before and during each pulse.

If the initial voltage difference between the Pulse on and Pulse off minus the next Pulse on and Pulse off
difference is more than 1.5 volts, the Oxygen Sensors are too cool and all testing is stopped. If the initial voltage
difference minus the next voltage difference is less than 1.5 volts, the Oxygen Sensors are properly heated and
the testing continues. Next, the cool-down phase begins. The PCM continues to pulse the Oxygen Sensor with 5
volts and then back to .45 volts. The PCM monitors and stores the first Pulse on and the first Pulse off voltages
and then subtracts them from each other. The PCM then subtracts the voltage difference from each new set of
Pulse on and Pulse off reads, to the difference of the voltage reads taken just before.

Once the PCM sees a difference between readings of at least .490 volts, the sensors have properly cooled and
the O2 Sensor Heaters are ready to be tested. If 3:40 minutes have elapsed and still a voltage difference of .490
has not been reached, the PCM begins heating the O2 Sensor that has cooled and disables testing on the O2
Sensor which has not fully cooled. If all Oxygen Sensors have cooled properly, the PCM then grounds the ASD
Relay (to provide the O2 Heaters with voltage). The PCM continues to Pulse 5 volts to all O2 Sensors after the
ASD Relay is turned on.

The O2 Heaters can pass by one of two methods: First, with the 5-volt Pulse on, the PCM compares to the next

1998 Chevrolet Pickup C1500

DRIVE CYCLES OBD-II Vehicles - OBD-II Readiness Monitors

5-Volt Pulse on value. If the voltages between spikes (on Pulses) has decreased by .157 volts. The O2 Heater
monitor passes and all testing is stopped this trip. Secondly, the voltage difference between the Pulse on voltage
is compared to next Pulse on voltage and is less than the prior voltage Pulse on, for 10 out of the 30 Pulses
(33%), this indicates a Heating Trend and the O2 Heater Passes. If neither a Heating Trend nor the Absolute
voltage is reached, the O2 Heater monitor fails 1 trip and the Freeze Frame Data is stored.

Misfire Monitor

Misfire monitor is continuously running during engine operation. For the Misfire monitor to be enabled, the
Adaptive Numerator must be learned since battery disconnect and every Key on there after (known as Power-on
learning). The Adaptive Numerator is a software learning routine that tells the PCM where the crankshaft slots
are. Since every crankshaft is different, the PCM must learn exactly where its particular crankshaft slots are;
otherwise its RPM calculations would be wrong. After a battery disconnect and then a power-up of the PCM,
the Adaptive Numerator is set to a value which it would be at if everything were perfect (crankshaft slots,
sensors, PCM hardware, etc.). If the Adaptive Numerator is equal to the default value, no learning has happened
and the Misfire Monitor will not run. To allow the PCM to learn the Adaptive Numerator, the following must
happen:

Open Throttle.

Engine Cool Temp Above 100°F; Or if below 100°F, Wait For ECT Rise Of 59°F.

More Than 10" Vacuum.

Above 1200 RPM.

Below 3000 RPM - A/T.

Below 3488 RPM - M/T.

Once the PCM has learned the Adaptive Numerator, the Misfire Monitor will run.

Fuel System Monitor

Fuel System monitor is continuously running during engine operation.

1995-2002 JTEC

OBD-II Monitor Enabling Criteria RWD/4WD JTEC PCM Equipped Vehicles

The following procedure has been established to assist technicians in the field with enabling and running OBD-
II Monitors on RWD/4WD trucks and Jeep models equipped with Jeep/Truck Engine Controller (JTEC). The
order listed in the following procedure is intended to allow the technician to effectively complete each monitor
and to set the CARB Readiness Status in the least time possible.

NOTE:

Once the monitor run process has begun, do not turn off the ignition. By
turning the ignition key off the monitor enabling conditions will be lost. Only the
O2 Heater Monitor runs after key off.

NOTE:

By performing a battery disconnect, or erasing diagnostic trouble codes, the

1998 Chevrolet Pickup C1500

DRIVE CYCLES OBD-II Vehicles - OBD-II Readiness Monitors

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