SERVICE MANUAL NUMBER 23
TROUBLE CODE DIAGNOSTICS - 454/502 MAG MPI & 8.2L MPI
Page 5F-24
90-861326--1 MARCH 1999
Code 21 (2 of 3): Throttle Position (TP) Sensor Circuit (Scan)
TEST DESCRIPTION:
Number(s) below refer to step number(s) on the diagnostic table.
Step 2: With throttle closed the TP sensor should read between .3 and .8 volt. If it does not,
check throttle cable adjustment or for bent linkage.
Step 4: With the TP sensor disconnected, the TP voltage should go low if the ECM and wir-
ing are OK.
Step 7: Probing CKT 813 with a DVOM to CKT 416 checks the sensor ground. A faulty sen-
sor ground will cause a Code 21.
STEP
ACTION
VALUE
YES
NO
PROCEED TO
1
Was the “On-Board Diagnostic” (OBD) System
Check Performed?
–
Step 2
Go to
OBD
System
Check
1. Throttle closed.
2. Ignition ON.
2
Does scan tool indicate throttle position
sensor voltage greater than 4 volts?
Step 5
Step 3
Does scan tool indicate throttle position
sensor voltage less than .36 volts?
Step 4
Step 3
3
Code 21 is intermittent, refer to “Diagnostic
Aids” on facing page.
–
–
–
1. Ignition OFF.
4
2. Disconnect throttle position sensor electrical
connector. Jumper throttle position sensor har-
ness terminals “A” and “C” together.
4
3. Ignition ON.
4. Scan tool should indicate throttle position
sensor voltage greater than 4 volts.
Does it?
–
Step 11
Step 6
1. Ignition OFF.
2 Disconnect throttle position sensor connec
5
2. Disconnect throttle position sensor connec-
tor.
5
3. Ignition ON.
Does scan tool indicate voltage over 4
Does scan tool indicate voltage over 4
volts?
–
Step 8
Step 7
1. Ignition OFF.
g
2 Connect DVOM between throttle position
6
2. Connect DVOM between throttle osition
sensor harness terminal “A” and ground.
3 Ignition ON
3. Ignition ON.
Is voltage over 4 volts?
–
Step 9
Step 10
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