Circuit Description
The Manifold Absolute Pressure (MAP) sensor responds to changes in intake manifold pressure (vacuum). The MAP sensor signal voltage to the PCM varies from below 2 volts at idle (high vacuum) to above 4 volts with the key ON, engine not running or at wide-open throttle (low vacuum). The MAP sensor is used to determine manifold pressure changes while the linear EGR flow test diagnostic is being run (refer to DTC P0401), to determine engine vacuum level for some other diagnostics and to determine barometric pressure (BARO). The PCM monitors the MAP signals for voltages outside the normal range of the MAP sensor. If the PCM detects a MAP signal voltage that is excessively high, DTC P0108 will be set.
Conditions for Setting the DTC
| • | No TP sensor DTCs present. |
| • | Engine has been running for a length of time that is determined by startup coolant temperature. The length of time ranges from 2 minutes at less than -30° C (-22° F) to 0.5 second at more than 30°C (86°F). |
| • | Throttle position below 2% |
| • | Engine speed is less than 900 rpm. |
| • | The MAP sensor signal voltage is greater than 4.2 volts. |
| • | Above conditions present for longer than 175 3X reference periods (58 crankshaft revolutions). |
Action Taken When the DTC Sets
| • | The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed. |
| • | The PCM will store conditions which were present when the DTC set as Freeze Frame and Failure Records data. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn OFF the MIL during the third consecutive trip in which the diagnostic has been run and passed. |
| • | The History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | The DTC can be cleared by using the scan tool. |
Diagnostic Aids
Check for the following conditions:
- Poor connection at PCM. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
- Damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the MAP display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the display will indicate the location of the fault.
If DTC P0108 cannot be duplicated, the information included in the Fail Records data can be useful in determining since the DTC was last set. If it is determined that the DTC occurs intermittently, performing DTC P1108 Diagnosis may isolate the cause of the fault.
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table:
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||
2 |
Is the MAP voltage greater than the specified value? | 3.5V | ||
3 |
Does scan tool indicate DTC P0108 failed? | -- | Refer to Diagnostic Aids | |
4 |
Is the MAP sensor voltage at the specified value? | 0V | ||
5 | Probe the sensor ground circuit with a test light to B+. Is the test light ON? | -- | ||
6 |
Was the MAP sensor signal circuit shorted? | -- | ||
7 |
Was a problem found? | -- | ||
8 | Check for a plugged or leaking vacuum supply to the MAP sensor. Is the vacuum supply OK? Was a problem found? | -- | ||
9 |
Was a problem found? | -- | ||
10 |
Was a problem found? | -- | ||
Replace the PCM. Important:: The replacement PCM must be programmed. Go to Powertrain Control Module Replacement/Programming . Is action complete? | -- | -- | ||
12 |
Was a problem found? | -- | ||
13 | Check for poor electrical connections at the MAP sensor and replace terminals if necessary. Refer to Wiring Repair in Electrical Diagnosis. Was a problem found? | -- | ||
14 | Replace the MAP sensor. Go to Manifold Absolute Pressure Sensor Replacement Is action complete? | -- | -- | |
15 | Repair the faulty vacuum source. Is action complete? | -- | -- | |
16 |
Does scan tool indicate DTC P0108 failed? | -- | System OK |
