SERVICE MANUAL NUMBER 24
DIAGNOSTICS
Code 34 (1 of 3): Manifold Absolute Pressure (MAP) Sensor Circuit
ECM
MEFI 2 MEFI 3
J1-31
J1-9
J2-19
J2-27
J2-18
MANIFOLD
PRESSURE
(VACUUM)
J1-29
814
BLK
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
1.0-2.0
volts at idle to about 4.0-5.0 volts at Wide Open Throttle (WOT).
If the MAP sensor fails, the ECM will substitute a default MAP value that will vary with rpm.
A reference voltage of 5 volts is provided to the MAP sensor through CKT 416. CKT 814 is
the ground circuit for the MAP sensor. MAP sensor CKT 432 will send a voltage signal to
the ECM proportional to the manifold pressure.
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
terminal 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 wiring harnesses related to the MAP sensor. A change in the MAP sensor dis-
play will indicate the location of the fault.
•
•
If the idle is rough or unstable, refer to “Troubleshooting” section for items which may
cause an unstable idle.
With the ignition ON, engine OFF, the manifold pressure is equal to atmospheric
pressure and the signal voltage will be high. This information is used by the ECM as
an indication of altitude and is referred to as BARO. Comparison of this BARO read-
ing, with a known good MAP sensor, is a good way to check the accuracy of a “sus-
pect” sensor. Reading should be the same, plus or minus 0.4 volt.
•
If DTC 14 is also set, check for open in ground CKT 814.
After repairs, clear DTC following “Clearing Trouble Codes ” procedure at the front of this
section. Failure to do so may result in DTC not properly being cleared.
Index
90-861327--1
OCTOBER 1999
Page 5G-71
| Categories | Mercury MerCruiser Manuals |
|---|---|
| Tags | Mercury MerCruiser 305 CID, Mercury MerCruiser 350 CID |
| Model Year | 1998, 1999, 2000, 2001 |
| Download File |
|
| Document File Type | |
| Copyright | Attribution Non-commercial |
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