Diagnostic Trouble Code (Dtc) P0121 Tp System Performance - Isuzu 1999 RODEO Workshop Manual

Diagnostic Trouble Code (DTC) P0121 TP System Performance

Circuit Description
The throttle position (TP) sensor circuit provides a voltage
signal that changes relative to throttle blade angle. The
signal voltage will vary from about 0.6 volts at closed
throttle to about 4.5 volts at wide open throttle (WOT).
The TP signal is one of the most important inputs used by
the powertrain control module (PCM) for fuel control and
many of the PCM-controlled outputs. The PCM monitors
throttle position and compares actual throttle position
from the TP sensor to a predicted TP value calculated
from engine speed. If the PCM detects an out-of-range
condition, DTC P0121 will set.
Conditions for Setting the DTC
f The engine is running.
f No MAP DTCs, or P0121, P0122, P1122, P0123 DTCs
are set.
f MAP reading is below 55 kPa.
f Throttle is steady, throttle angle is changing less than
1%.
f Predicted throttle angle is not close to actual throttle
angle.
f Above conditions are present for a total of 12.5
seconds over a 25-second period of time.
Action Taken When the DTC Sets
f The PCM will illuminate the malfunction indicator lamp
(MIL) after the second consecutive trip in which the
fault is detected.
RODEO 6VD1 3.2L ENGINE DRIVEABILITY AND EMISSIONS
f The PCM will store conditions which were present
when the DTC was set as Freeze Frame and in the
Failure Records data.
f The PCM will use a default throttle position based on
mass air flow and RPM.
Conditions for Clearing the MIL/DTC
f The PCM will turn the MIL "OFF" on the third
consecutive trip cycle during which the diagnostic has
been run and the fault condition is no longer present.
f A history DTC P0121 will clear after 40 consecutive
warm-up cycles have occurred without a fault.
f DTC P0121 can be cleared by using the Tech 2 "Clear
info " function or by disconnecting the PCM battery
feed.
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 EGR
Valve.
If these codes are also set, it could indicate a
problem with the 5 Volt reference circuit or
components itself.
f The TP Sensor share a ground with the EGR Valve and
the IAT Sensor.
6E2–149
D06RW059