Code 21 (1 Of 2): Throttle Position (Tp) Sensor Circuit (Scan) High Signal Voltage; Voltage - Mercury MerCruiser MCM 454 Mag MPI Service Manual

SERVICE MANUAL NUMBER 23
Code 21 (1 of 2): Throttle Position (TP) Sensor Circuit (Scan) High Signal

Voltage

CIRCUIT DESCRIPTION:
The Throttle Position (TP) Sensor provides a voltage signal that changes as throttle blades
open or close. Signal voltage should vary from about .7 volts at idle to about 4.5 volts at Wide
Open Throttle (W.O.T.).
The TP signal is one of the most important inputs used by the Electronic Control Module
(ECM) for fuel control and for most of the ECM controlled outputs.
The ECM supplies a 5 volt signal to the sensor through CKT 416. CKT 813 is the TP sensor
ground circuit. The TP sensor will send a voltage signal back to the ECM, through CKT 417,
according to where the throttle blades are positioned.
DIAGNOSTIC AIDS:
Check for the following conditions:
After repairs, clear DTC's following "Clearing Trouble Codes" procedure at the front of this
section. Failure to do so may result in DTC's not properly being cleared.
Index
90-861326--1 MARCH 1999
Downloaded from https://needmanual.com/
b
i
B
a
C
C
h
A
A
a - Throttle Position Sensor
b - Front View Of Connector
c - To IAT Sensor
d - To Map Sensor
e - Sensor Ground
f - TP Signal
g - 5V Reference
h - Wide Open Throttle
i - Idle
Poor connection at ECM. Inspect harness connectors for backed out terminals,
improper mating broken locks, improperly formed or damaged terminals, and poor ter-
minal to wire connection.
Damaged harness. Inspect the wiring harness for damage. If the harness appears to be
OK, observe the TP sensor display on the scan tool while moving connectors and wiring
harnesses related to the TP sensor. A change in the TP sensor display will indicate the
location of the fault.
The scan tool reads throttle position in voltage and percentage relative to the throttle
blade opening. With ignition "ON," engine "OFF," throttle blades closed (idle), the volt-
age should be 0.3-0.9 volts. The voltage should steadily increase as the throttle is
moved toward Wide Open Throttle (WOT).
c
B
d
TROUBLE CODE DIAGNOSTICS - 7.4L MPI
e
f
g
Page 5G-43