Mercury MerCruiser MCM 454 Mag MPI Service Manual page 726

SERVICE MANUAL NUMBER 23
Code 33 (2 of 3): Manifold Absolute Pressure (MAP) Sensor Circuit (Scan)
TEST DESCRIPTION:
Number(s) below refer to step number(s) on the diagnostic table.
Step 4. Engine misfire or a low, unstable idle may set Code 33. Disconnect MAP sensor and
system will go into backup mode. If the misfire or idle condition remains, refer to "Trouble-
shooting."
Step 5. If the ECM recognizes the low MAP signal, the ECM and wiring are OK.
NOTE: If engine is idling rough, unstable or incorrect, this condition must be corrected be-
fore proceeding (refer to troubleshooting section).
Index
90-861326--1 MARCH 1999
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STEP
Was the "On-Board Diagnostic" (OBD) System
1
Check Performed?
2 Engine idling
Does scan tool display a MAP sensor volt-
age of less than 1 volt?
Does scan tool display a MAP sensor volt-
age of greater than 4 volts?
Code 33 is intermittent, if not additional codes
3
were stored, refer to "Diagnostic Aids" on fac-
ing page.
4 1. Ignition OFF.
2. Disconnect MAP sensor electrical con-
nector.
3. Jumper MAP sensor harness terminals
"B" and "C" together.
4. Start engine.
Does scan tool display a MAP sensor volt-
age of greater than 4 volts?
5 1. Ignition OFF.
2. Disconnect MAP sensor electrical con-
nector.
3. Start engine.
Does scan tool display a MAP sensor volt-
age of less than 1 volt?
6 1. Ignition OFF.
2. Connect DVOM between MAP sensor
harness terminal "C" and "A."
3. Ignition ON.
I s voltage over 4 volts?
TROUBLE CODE DIAGNOSTICS - 454/502 MAG MPI & 8.2L MPI
ACTION VALUE YES NO
PROCEED TO
Go to
OBD
– Step 2
System
Check
– Step 4 Step 3
– Step 5 Step 3
– –
– Step 9 Step 6
– Step 7 Step 8
– Step 11 Step 10
Page 5F-29
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