Hummer H1 Service Manual page 1099

34 PCM/Tech 1 Scan Tool
DTC P0121 - Accelerator Pedal Position (APP) Sensor 1 Circuit Performance
Step
1 Important: Before clearing DTC(s) use the scan tool "Capture Info" to
record Freeze Frame and Failure Record for reference, as data will be lost
when "Clear Info" function is used.
Was the "On-Board Diagnostic (OBD) System Check" performed?
2 1. Ignition "ON", engine "OFF".
2. With the throttle closed, observe APP voltages on the scan tool.
Are APP voltages at specified values?
3 DTC is intermittent. If no additional DTCs are stored, refer to "Diagnostic
Aids". If additional DTCs were stored, refer to those chart(s).
4 1. Disconnect the APP sensor electrical connector.
2. Ignition "ON", engine "OFF".
3. With J–39200 connected to ground, probe APP sensor 5 volt reference
circuits at APP harness terminals "G", "D" and "E".
Is voltage at the specified value on all circuits?
5 1. Ignition "ON", engine "OFF".
2. With a test light connected to B+, probe APP sensor ground circuits at
the APP sensor harness terminals "A", "B" and "J".
Is Test light ON (all circuits)?
6 1. Ignition "OFF".
2. Disconnect the PCM and check the 5 volt reference circuit for an open or
short to ground.
3. If the 5 volt reference circuit is open or shorted to ground, repair as nec-
essary.
Was the 5 volt reference circuit open or shorted to ground?
7 Check the 5 volt reference circuit for a poor connection at the PCM and
replace terminal if necessary.
Did the terminal require replacement?
8 1. Ignition "OFF".
2. Disconnect the PCM, and check for an open sensor ground circuit to the
PCM.
3. If problem is found, repair as necessary.
Was APP sensor ground circuit open?
9 Replace the APP module.
Is Action complete?
10 Replace the faulty PCM. Notice: If the PCM is faulty, the new PCM must
be programmed. Go to PCM replacement and programming procedures.
Is the action complete?
11 1. Using the Scan Tool, select "DTC", "Clear Info".
2. Start engine and idle at normal operating temperature.
3. Select "DTC", "Specific", then enter the DTC number which was set.
4. Operate vehicle within the conditions for setting this DTC as specified in
the supporting text.
Does the Scan Tool indicate that this diagnostic Ran and Passed?
12 Using the Scan Tool, select "Capture Info", "Review Info".
Are any DTCs displayed that have not been diagnosed?
_____________________________________________________
Action Value(s) Yes
— Go to Step 2. Go to OBD Sys-
.45-.95v Go to Step 3. Go to Step 4.
4.0-4.5v
3.6-4.0v
— Go to the
applicable
DTC table.
4.75v Go to Step 5. Go to Step 6.
— Go to Step 9.
— Go to Step 11. Go to Step 8.
— Go to Step 11. Go to Step 10.
— Go to Step 11. Go to Step 10.
— Go to Step 11.
— Go to Step 11.
— Go to Step 12. Go to Step 2.
— Go to the
applicable
DTC table
®
No
tem Check.
Go to
Diagnostic
Aids.
Go to Step 8.
—
—
System OK