90-823225--1 10965E-92 - ELECTRONIC FUEL INJECTION (MULTI-PORT AND THROTTLE BODY)
Code 33: Manifold Absolute Pressure (MAP) Sensor Circuit (Non-Scan)
(1 Of 2)
814 BLK
MAP AND
ECT
GROUND
ECT SENSOR
CIRCUIT DESCRIPTION:
The Manifold Absolute Pressure (MAP) sensor re-
sponds to changes in manifold pressure (vacuum).
The ECM receives this information as a signal volt-
age that will vary from about 1-1.5 volts at closed
throttle idle, to 4-4.8 volts at Wide Open Throttle
(W.O.T.) (low vacuum).
If the MAP sensor fails, the ECM will substitute a fixed
MAP value and use the engine RPM to control fuel
delivery.
TEST DESCRIPTION:
Number(s) below refer to circled number(s) on the
diagnostic chart.
1. This step will determine if there is an adequate
vacuum supply to the MAP sensor. If the gauge
reading is erratic, refer to “Stalling, Rough, Un-
stable or Incorrect Idle” in “Troubleshooting.”
2. Low manifold vacuum may result from vacuum
leaks in the engine induction system.
3. This step checks for a voltage from terminal “C”
(5 volt reference) to terminal “A” (sensor ground).
4. This step will identify if the problem is in the sup-
ply 5 V reference or ground circuit.
5. This step determines if the MAP signal circuit to
the ECM is open.
6. This step completes the test for the ECM and wir-
ing. If the test light is not ON, the MAP sensor has
an internal problem. To confirm an internal MAP
sensor problem, use the MAP output voltage
check chart.
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 14 is also set, check for open ground CKT 814.
ALTITUDE
MAP SENSOR
VOLTAGE
RANGE
Feet Meters
Below 1,000 Below 305 3.8-5.5 V
1,000-2,000 305-610 3.6-5.3 V
2,000-3,000 610-914 3.5-5.1 V
3,000-4,000 914-1219 3.3-5.0 V
4,000-5,000 1219-1524 3.2-4.8 V
5,000-6,000 1524-1829 3.0-4.6 V
6,000-7,000 1829-2133 2.9-4.5 V
7,000-8,000 2133-2438 2.8-4.3 V
8,000-9,000 2438-2743 2.6-4.2 V
9,000-10,000 2743-3048 2.5-4.0 V
LOW ALTITUDE = HIGH PRESSURE = HIGH VOLTAGE
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