Voltage Low - Mercury MerCruiser MCM 454 Mag MPI Service Manual

SERVICE MANUAL NUMBER 23
Code 22 (1 of 2): Throttle Position (TP) Sensor Circuit (Non-Scan) Signal

Voltage Low

CIRCUIT DESCRIPTION
The throttle position (TP) sensor is a potentiometer that provides a voltage signal that
changes relative to the throttle blade. Signal voltage should vary from .7 volt at idle to 4.8
volts at wide open throttle (WOT).
The TP sensor signal is one of the most important inputs used by the ECM for fuel control
and for IAC control.
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.
TEST DESCRIPTION
STEP 2. This step simulates a trouble code 21. If the ECM recognizes the high signal voltage
and sets a trouble code 21, the ECM wiring are OK.
STEP 3. This step checks CKT 416 for the 5 volt reference.
Index
90-861326--1 MARCH 1999
Downloaded from https://needmanual.com/
b
i
B
a
C
C
h
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.
If DTC 34 is also set, check for a short to ground in CKT 416 or CKT 416E.
c
B
A
d
TROUBLE CODE DIAGNOSTICS - 7.4L MPI
e
f
g
Page 5G-11