TROUBLE CODE DIAGNOSTICS - 7.4L MPI
SERVICE MANUAL NUMBER 23
90-861326--1 MARCH 1999
Page 5G-53
Code 33 (2 of 3): Manifold Absolute Pressure (MAP) Sensor Circuit (Scan)
High Signal Voltage
TEST DESCRIPTION:
Number(s) below refer to step number(s) on the diagnostic table.
Step 2. This step will determine if there is an adequate vacuum supply to the MAP
sensor. If the vacuum gauge reading is erratic, refer to the “Rough or Unstable Idle” in
Troubleshooting section.
Step 4. This step simulates a DTC 34. If the ECM recognizes the low signal voltage and
sets a DTC 34, the ECM and wiring are OK.
Step 5. This step checks for an open in ground CKT 814.
STEP
ACTION
VALUE
YES
NO
PROCEED TO
1
Was the “On-Board Diagnostic” (OBD) System
Check Performed?
–
Step 2
Go to
OBD
System
Check
2
1. Ignition “OFF.”
2. Install a vacuum gauge to manifold vacu-
um.
14 in.
HG
3. Start engine and raise RPM to 1000.
HG
(45.5
4. The vacuum reading should be steady.
(45.5
kPa)
Is the vacuum reading steady and above
the specified value?
Step 3
Step 6
3
Allow the engine to idle.
Does the scan tool indicate MAP sensor
voltage greater than the specified value?
4 Volts
Step 4
Step 7
4
1. Ignition “OFF.”
2. Disconnect MAP sensor harness connec-
tor.
3. Ignition “ON,” engine “OFF.”
Does the scan tool indicate MAP sensor
voltage less than the specified value?
1 Volt
Step 5
Step 8
5
1. Ignition “OFF.”
2. Connect DVOM from harness terminal
“A” (CKT 814) to harness terminal “C” (CKT
416E).
3. Ignition “ON,” engine “OFF.”
Does the scan tool indicate MAP sensor
voltage greater than the specified value?
4 Volts
Step 10
Step 9
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