TROUBLE CODE DIAGNOSTICS - 7.4L MPI
SERVICE MANUAL NUMBER 23
Page 5G-22
90-861326--1 MARCH 1999
Code 34 (1 of 3): Manifold Absolute Pressure (MAP) Sensor Circuit (Non-Scan)
Low Signal Voltage
814 BLK
a
b
c
d
e
a -
Manifold Absolute Pressure (Vacuum)
b -
To ECT Sensor
c -
To TP Sensor
d -
Map Signal
e -
Map And ECT Ground
CIRCUIT DESCRIPTION:
The Manifold Absolute Pressure (MAP) sensor responds to changes in manifold pressure
(vacuum). The ECM receives this information as a signal voltage that will vary from about
1.0-1.5 volts at idle to about 4.0-4.5 volts at Wide Open Throttle (WOT).
If the MAP sensor fails, the ECM will substitute a default MAP value that will vary with RPM.
The MAP sensor voltage of 5 volts is delivered to the MAP sensor through CKT 416E. CKT
814 is the ground circuit for the MAP sensor. The MAP signal CKT 432 will send a voltage
signal back to the ECM according to what the manifold pressure is.
DIAGNOSTIC AIDS:
Check for the following conditions:
•
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 MAP sensor display on the scan tool while moving connectors and wir-
ing harnesses related to the MAP sensor. A change in the MAP sensor display will indi-
cate the location of the fault.
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