Pontiac Fiero 1988 Service Manual page 487

6E2-A-32 DRIVEABILITY AND EMISSIONS - FUEL INJECTION (TBI)
THROTTLE
POSITION
SENSOR
THROTTLE
POSITION
SENSOR
CONNECTOR
TO MAP SENSOR
ECM
416GRA
417 DK BLU
452 BLK
W11
B19
B12
TO COOLANT SENSOR
5 5-87
- 5V REF
h— TPS SIGNAL
.SENSOR
— GROUND
4-29-87
* 7S 3206-6EA
CODE 21
THROTTLE POSITION SENSOR (TPS) CIRCUIT
(SIGNAL VOLTAGE HIGH)
2.5L " P " SERIES (TBI)
Circuit Description:
The throttle position sensor (TPS) provides a voltage signal that changes relative to the throttle valve.
Signal voltage will vary from less than 1.25 volts at idle to about 4.5 volts at wide open throttle (WOT).
The TPS signal is one of the most important inputs used by the ECM for fuel control and for many of the
ECM controlled outputs.
Test Description.
Numbers below refer to circled
numbers on the diagnostic chart.
1. This step checks to see if Code 21 is the result of a
hard failure or an intermittent condition.
A Code 21 will set if:
• TPS reading above 2.5 volts.
• Engine speed less than 1800 rpm.
• MAP reading below 60 kPa.
• All of the above conditions present for 2
seconds.
2. This step simulates conditions for a Code 22. If
the ECM recognizes the change of state, the ECM
and CKTs 416 and 417 are OK.
3. This step isolates a faulty sensor, ECM, or an open
CKT 452. If CKT 452 is open, there may also be a
Code 15 stored.
Diagnostic Aids:
A "Scan" tool displays throttle position in volts.
Closed throttle voltage should be less than 1.25 volts.
TPS voltage should increase at a steady rate as
throttle is moved to WOT.
A Code 21 will result if CKT 452 is open or CKT
417 is shorted to voltage. If Code 21 is intermittent,
refer to Section "B".