Skylark L4-144 2.4L DOHC VIN T SFI (1997)
Throttle Position Sensor: Technical Service Bulletins
Engine Controls - Revised DTC P0121 Diagnosis
File In Section: 6E Engine Fuel & Emission
Bulletin No.: 61-65-44
Date: September, 1996
SERVICE MANUAL UPDATE
Subject:
Section SE - Engine Controls Revised DTC P0121 Diagnostic Support information
Models:
1997 Buick LeSabre, Park Avenue, Riviera, Skylark
1997 Chevrolet Camaro, Lumina, Monte Carlo, Venture
1997 Oldsmobile Achieva, Cutlass Supreme, Eighty Eight, LSS, Regency, Silhouette
1997 Pontiac Bonneville, Firebird, Grand Am, Trans Sport with 3.1 L, 3.4L, 3.8L Engines (VINs 1, E, K, M, X - RPOs L36, L67, L82, LA1, LQ1)
This bulletin is being issued to revised the DTC PO121 - TP Sensor Performance diagnostic support information in Engine Controls, Section 6E. The
DTC PO121 diagnostic checks for a high TP sensor signal condition during low MAP signal situations and a low TP sensor condition during high MAP
signal situations. This bulletin includes additional information required to identify and diagnose a low TP sensor signal condition.
3.1L (VIN M) 3.4L (VIN E, X)
Conditions for Setting the DTC
^
No TP or MAP sensor DTCs set.
^
The engine is running.
^
The MAP reading is less than 55 kPa (TP sensor high test) or greater than 70 kPa (TP sensor low test).
^
The throttle angle is steady.
^
The predicted throttle angle (based on engine speed) is not close to actual throttle angle.
^
The above conditions are present for at least 10 seconds.
Diagnostic Aids
The Scan tool will not display a passed status for the DTC P0121 diagnostic test until the PCM completes both the stuck high (high TP angle during a
low MAP situation) and the stuck low (low TP angle during a high MAP situation) portions of the test. When verifying a repair or otherwise attempting
to monitor the DTC P0121 diagnostic, refer to Conditions for Setting the DTC for the MAP signal levels required to complete both parts of the
diagnostic.
Check for the following conditions:
^
Vacuum hoses disconnected or vacuum leaks. Visually and physically check for the following conditions:
-
Disconnected vacuum hoses. Refer to Emission Hose Routing Diagram.
-
Damaged vacuum hoses. Refer to Emission Hose Routing Diagram.
-
Incorrect vacuum hoses routing. Refer to Emission Hose Routing Diagram.
-
Damaged fuel injector 0-rings. Refer to Fuel Injector.
-
Damaged gasket at the throttle body, intake manifold, PCV valve cover, EGR pipes, or EGR valve mounting surface.
-
Incorrectly installed or malfunctioning PCV valve. Refer to Positive Crankcase Ventilation Valve.
^
Damaged or sticking throttle plate or IAC valve. A throttle plate or IAC valve that allows too much airflow with the throttle closed may cause a high
idle and DTC P0121 to set. Refer to Idle Air Control System Check for diagnosis.
^
Incorrect 3X reference signal. A condition that causes an incorrect 3X reference signal may cause the MAP sensor value to stop updating. This
condition can cause DTC P0121 to be set during a closed throttle condition. An incorrect 3X reference signal should cause DTC P1374 to be set. If
DTC P1374 and DTC P0121 are set, diagnose DTC P1374 first.
^
Stuck open EGR valve. An EGR valve stuck partially open may cause the TP sensor low test to fail and DTC P0121 to set. A sticking EGR valve
