Mercury MerCruiser MCM 454 Mag MPI Service Manual page 789

TROUBLE CODE DIAGNOSTICS - 7.4L MPI
Code 21 (2 of 2): Throttle Position (TP) Sensor Circuit (Scan) High Signal
Voltage
TEST DESCRIPTION:
Number(s) below refer to step number(s) on the diagnostic table.
Step 2. With the throttle closed, the TP sensor voltage should read 0.3-0.9 volt. If it does
not, check the throttle cable adjustment or for bent or binding linkage.
Step 3. This test simulates a DTC 22. If the ECM recognizes the low voltage signal, the
ECM and wiring are OK.
Step 4. Using DVOM from harness terminal "A" (CKT 416) harness terminal "B." (CKT
813) checks the sensor ground circuit. A faulty sensor ground CKT 813 will cause a DTC
21.
STEP
1
2
3
4
5
6
7
8
9
Index
Page 5G-44
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ACTION
Was the "On-Board Diagnostic" (OBD) System
Check Performed?
1. Throttle closed.
2. Ignition "OFF".
Does scan tool indicate TP sensor voltage
greater than the specified value?
1. Ignition "OFF"
2. Disconnect TP sensor harness connec-
tor.
3. Ignition "ON, engine "OFF".
Does scan tool indicate TP sensor voltage
less than the specified value?
Connect DVOM from harness terminal "A"
(CKT 416) to harness terminal "B" (CKT 813).
Does scan tool indicate TP sensor voltage
greater than the specified value?
Trouble code 21 is intermittent. Locate and
repair intermittent faulty connections.
Locate and repair short to voltage in CKT 417.
If a problem was found, repair as necessary.
Was a problem found?
Locate and repair open in ground CKT 813. If
a problem is found, repair as necessary. Was a
problem found?
Replace faulty TP Sensor. Is action complete?
Repair faulty ECM connections or replace
faulty ECM. Is action complete?
SERVICE MANUAL NUMBER 23
VALUE YES NO
PROCEED TO
Go to
OBD
– Step 2
System
Check
4 Volts Step 3 Step 5
.3 Volt Step 4 Step 6
4 Volts Step 7 Step 8
– –
– Step 9
Verify
– Step 9
Repair
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–
90-861326--1 MARCH 1999
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