DTC 33

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

A Tech 1 "Scan" tool 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.

MAP Sensor Diagnostic Chart:

Test Description
Number(s) below refer to circled number(s) 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 Rough, Unstable, or Incorrect Idle, Stalling for 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 of a "suspect" sensor. Reading should be the same 1.4 volt.

If MAP sensor is suspected to be faulty, Chart C-1D Manifold Absolute Pressure (MAP) Output Check - Intermittent Malfunctions