DTC 33

Code 33 - MAP Sensor Circuit (Signal Voltage High - Low Vacuum):

Wiring Diagram For Code 33 - MAP Sensor Circuit (Signal Voltage High - Low Vacuum):

CODE 33 - MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR CIRCUIT

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 1-1.5 volts at idle to 4-4.5 volts at Wide Open Throttle (WOT). Signals will vary depending on altitude.

A "Scan" displays manifold pressure in volts. Low pressure (high vacuum) reads a low voltage while a high pressure (low vacuum) reads a high voltage.

If the MAP sensor fails the ECM will substitute a fixed MAP value and use the Throttle Position Sensor (TPS) to control fuel delivery.



Test Description: Numbers below refer to circled numbers on the diagnostic chart.

1. Code 33 will set when:

^ Signal is too high (kPa greater than 80 kPa)
^ TPS less than 4%
^ Engine is running
^ No Code 21 or Code 22
^ Vehicle speed is less than 2 mph
^ All conditions met for more than 5 seconds
Engine misfire or a low unstable idle may set Code 33.

2. If the ECM recognizes the low MAP signal, the ECM and wiring are OK.


Diagnostic Aids:

If idle is rough or unstable refer items which can cause an unstable idle.

An open in CKT 455 or the connection will result in a Code 33.

With the ignition "ON," and the engine stopped, 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 vehicle altitude and is referred to as BARO. Comparison of this BARO reading with a known good vehicle with the same sensor is a good way to check accuracy suspect" sensor. Reading should be the same +/- .4 volt.

If MAP sensor is suspected to be faulty, refer to CHART C-1D.

See Diagnosis By Symptoms - No Trouble Codes Stored.