Mercury 305 CID, Service Manual, Page: 631 / 967

90-823225--1 1096 5E-90 - ELECTRONIC FUEL INJECTION (MULTI-PORT AND THROTTLE BODY)
Code 21: Throttle Position (TP) Sensor Circuit (Non-Scan)
(1 Of 2)
TP
B
C
A
A
C
B
CIRCUIT DESCRIPTION:
The Throttle Position (TP) sensor provides a voltage
signal that changes, relative to the throttle blade. Sig-
nal voltage should vary from about .7 volts at idle to
about 4.5 volts at Wide Open Throttle (W.O.T.).
TEST DESCRIPTION:
Number(s) below refer to circled number(s) on the
diagnostic chart.
1. This step checks for a voltage from terminal “C”
(5 volt reference) to terminal “A” (sensor ground).
2. This step will identify if the problem is in the sup-
ply or ground circuit.
3. This step determines if the TP sensor signal cir-
cuit to the ECM is open.
4. This step completes the test for the ECM and wir-
ing. If the test light is not ON, the TP sensor has
an internal problem.
DIAGNOSTIC AIDS:
An intermittent problem may be caused by a poor or
corroded connection, rubbed through wire connec-
tion, a wire that is broken inside the insulation, or a
corroded wire.
Any circuitry that is suspected as causing the inter-
mittent complaint should be thoroughly checked for
backed-out terminals, improper mating, broken
locks, improperly formed or damaged terminals, poor
terminal-to-wiring connections, corroded terminals
and/or wiring, or physical damage to the wiring har-
ness. After repairs, clear codes following “Clearing
Codes” in “ECM Self-Diagnostics.” Failure to do so
may result in codes not properly being cleared. If
Code 23 is also set, check CKT 813 for faulty wiring
or connections. Check terminals at sensor for good
contact.