Circuit Description
The Manifold Absolute Pressure (MAP) sensor responds to changes in the manifold pressure (vacuum). The ECM receives this information as a signal voltage that will vary from about 1.0 to 1.5 volts at idle from 4.0 to 4.8 volts at a wide open throttle (low vacuum).
Conditions for Setting the DTC
| • | Engine running |
| • | Manifold pressure greater than 68 kPa (A/C OFF) |
| • | Throttle angle less than 4% |
| • | Conditions met for 5 seconds |
| • | Engine misfire or a low, unstable idle may set DTC 33 |
Action Taken When the DTC Sets
If the MAP sensor fails, the ECM will substitute a fixed MAP value. The ECM uses the Throttle Position (TP) sensor in order to control the fuel delivery and turns ON the MIL (Malfunction Indicator Lamp).
Conditions for Clearing the MIL/DTC
The conditions for the fault are no longer present and 50 ignition cycles have passed with no further faults or the ignition switch is turned OFF and the battery feed voltage is removed for 10 seconds.
Diagnostic Aids
An engine misfire, a low unstable idle, or a manifold vacuum below 51 kPa (15 in Hg) may set the DTC 33. Disconnect the MAP sensor and system will go into the backup mode. If the misfire or idle condition remains, refer to Symptoms .
Refer to Intermittent Conditions .
With the ignition ON and the engine stopped, the manifold pressure should equal the atmospheric pressure and the signal voltage will be high. The ECM uses this information as an indication of vehicle's altitude. Comparison of this reading with a known good vehicle with the same sensor is a good way to check the accuracy of a suspect sensor. The readings should be the same plus or minus 0.4 volt.
Important: Make sure the electrical connector remains securely fastened.
| • | Check all connections. |
| • | Disconnect the sensor from the bracket, and twist the sensor by hand only in order to check for intermittent connections. The output changes greater than 0.1 volt indicates a bad connector or connection. If OK, replace sensor. |
| • | Refer to Manifold Absolute Pressure Sensor Output Check Diagnosis for further diagnosis. |
Test Description
The numbers below refer to the step numbers on the Diagnostic Table.
-
Checks to see if DTC was set as result of a hard failure or intermittent condition.
-
With the MAP sensor disconnected the ECM should see a low voltage if the ECM and wiring is OK.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the On-Board Diagnostic (OBD) System Check? | -- | ||
2 | Does the engine run rough, unstable or incorrect? | -- | ||
Does the scan tool display a MAP voltage greater than the specified value? | 4.0 V | Go to Diagnostic Aids | ||
Does the scan tool display a MAP voltage less than the specified value? | 1.0 V | |||
5 |
Did you find a problem? | -- | ||
6 |
Did you find a problem? | -- | Go to Step | |
7 | Probe the sensor ground circuit with a test lamp connected to B+. Is the test lamp ON? | -- | ||
8 | Repair the open sensor ground circuit. Is the action complete? | -- | -- | |
9 |
Did you a problem? | -- | ||
10 |
Is the action complete? | -- | -- | |
11 | Replace the ECM. Refer to Engine Control Module Replacement . Is the action complete? | -- | -- | |
12 |
Did the DTC reset? | -- | ||
13 | Are any DTCs stored which you have not diagnosed? | -- | Go to the Applicable DTC Table | System OK |
