Isuzu 1999 RODEO Workshop Manual page 760

Diagnostic Aids
Check for the following conditions:
f Skewed MAP signal or faulty MAP sensor – An
incorrect MAP signal may cause the PCM to incorrectly
calculate the predicted TP sensor value during high
engine load situations. Check for an unusually low
MAP reading. This condition can cause DTC P0121 to
be set.
f The TP sensor shares a 5 Volt reference with the MAP
sensor and Fuel Pressure sensor.
If these codes are also set, it could indicate a
problem with the 5 Volt reference circuit.
f The TP sensor shares a ground with the MAP sensor
and the Fuel Pressure sensor.
f Poor connection at PCM – Inspect harness connectors
for backed–out terminals, improper mating, broken
DTC P0121 TP Sensor/Range Performance Problem
Step
1 Was the "On–Board Diagnostic (OBD) System Check"
performed?
2 1. Ignition ON engine OFF
2. Review and record Tech 2 Failure Records data,
then clear the DTC's.
3. Operate the vehicle within Failure Records
conditions as noted.
4. Using a Tech 2, monitor "DTC" info for DTC P0121.
Does the Tech 2 indicate that DTC P0121 "Ran and
Passed?"
3 1. Ignition ON, engine OFF.
2. Monitor the TP value on the Tech 2 while moving the
throttle between 0% and 100%.
Does the TP value on the Tech 2 move smoothly from
0% (0.25 volts) to 100% (4.75 volts)? (if no, start with
the diagnosis chart for other sensors in the circuit and
see if 5V returns.)
4 1. Ignition OFF.
2. Disconnect the Throttle Position (TP) Sensor
electrical connector, located on the RH side of the
Throttle body.
3. Start the vehicle, and monitor the TP value with the
Tech 2.
Does the TP value on the Tech 2 hold steadily within the
given range?
5 Check the TP sensor signal circuit; between the TP
sensor and the Powertrain Control Module (PCM), for a
short to voltage.
Was the problem found?
6 Check the TP sensor circuit, between the TP sensor
and the PCM, the following conditions:
f
A short to ground
f
An open circuit
Was the problem found?
RODEO X22SE 2.2L ENGINE DRIVEABILITY AND EMISSION
Action
locks, improperly formed or damaged terminals, and
poor terminal–to–wire connection.
f Damaged harness – Inspect the wiring harness for
damage; an open circuit, a short to ground, or a short
to voltage. If the harness appears to be OK, observe
the MAP display on the Tech 2 while moving
connectors and wiring harnesses related to the sensor.
A change in the display will indicate the location of the
fault.
If DTC P0121 cannot be duplicated, the information
included in the Failure Records data can be useful in
determining vehicle mileage since the DTC was last set. If
it is determined that the DTC occurs intermittently,
performing the DTC P1122 or P1121 Diagnostic Chart
may isolate the cause of the fault.
Value(s)
— Go to Step 2
Diagnostic
—
— Go to Step 4
0–0.25 volts
0% Go to Step 6
— Verify repair
— Verify repair
6E1–133
Yes No
Go to OBD
System
Check
Refer to
Aids Go to Step 3
Go to Step 11
Go to Step 5
Go to Step 12
Go to Step 7