Grand AM L4-144 2.4L DOHC VIN T SFI (1997)
should cause DTC P1406 to set. If DTC P1406 and DTC P0121 are set, diagnose DTC P1406 first.
^
Restricted exhaust system. Refer to Restricted Exhaust System Check.
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Skewed MAP signal or malfunctioning MAP sensor. An incorrect MAP signal may cause the PCM to incorrectly calculate the predicted TP sensor
value during high engine load or closed throttle situations. Check for the following conditions:
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an unusually low MAP reading with the key ON, engine not running.
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an unusually high MAP reading at idle.
Either condition can cause DTC P012l to set.
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Poor connection at the PCM. Inspect harness connectors for the following conditions
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Backed out terminals.
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Improper mating
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Broken locks.
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Improperly formed or damaged terminals.
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Poor terminal to wire connection.
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Damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the ECT display on the scan tool while moving
connectors and wiring harnesses related to the sensor. A change in the display will indicate the location of the malfunction.
If DTC P0121 cannot be duplicated, the information included in the Fail Records data can be useful in determining vehicle mileage since the DTC was
last set. If the DTC occurs intermittently, performing the DTC P1122 or DTC P1121 Diagnostic Charts may isolate the cause of the malfunction.
3800 (VIN 1, K)
Conditions for Setting the DTC
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No TP or MAP sensor DTCs set.
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The engine is running.
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The idle air control valve position is between 0 and 130 counts.
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The MAP reading is less than 50 kPa (TP sensor high test) or greater than 70 kPa (TP sensor low test).
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The throttle angle is steady.
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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:
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Disconnected vacuum hoses. Refer to Emission Hose Routing Diagram.
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Damaged vacuum hoses. Refer to Emission Hose Routing Diagram.
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Incorrect vacuum hoses routing. Refer to Emission Hose Routing Diagram.
