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 active TP sensor DTC present. |
| • | Engine running. |
| • | Throttle position below 30% if engine speed is below 3000 RPM. |
| • | Throttle position below 2% if engine speed is above 3000 RPM. |
| • | The MAP sensor signal voltage is greater than 3.5V. |
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:
| • | Monitor the MAP sensor using the scan tool. If the MAP sensor does not respond to throttle changes, check the 3X circuits from the ignition control module to the PCM. |
| If the 3X signal is lost the PCM will only update the MAP sensor reading once per key cycle, when the engine is first started. |
| Depending on where the MAP sensor voltage (high voltage or low voltage) is when the engine is started, the high or low voltage MAP sensor DTC's will set. |
| • | 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 the DTC P1108 Diagnostic Chart 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 System Check performed? | -- | Go to Powertrain OBD System Check | |
2 |
Is the MAP voltage above the specified value? | 3.5V | ||
3 |
Does scan tool indicate DTC P0108 failed? | -- | Go 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? | -- | ||
9 |
Did the terminal require replacement? | -- | ||
10 | Check continuity of the MAP sensor ground circuit. If the MAP sensor ground circuit measures over 5 ohms, repair open or poor connection. Refer to Repair Procedures in Electrical Diagnosis section 8A. Was a condition found and corrected? | -- | ||
Replace the PCM. Important: The replacement PCM must be programmed. Refer to PCM Replacement/Programming. Is action complete? | -- | -- | ||
12 |
Was the 5 volt reference A circuit shorted? | -- | ||
13 | Check for poor electrical connections at the MAP sensor and replace terminals if necessary. Refer to Repair Procedures in Electrical Diagnosis section 8A. Did any terminals require replacement? | -- | ||
14 | Replace the MAP sensor. Is Action complete? | -- | -- | |
15 | Repair the faulty vacuum source. Is action complete? | -- | -- | |
16 |
Does scan tool indicate DTC P0108 failed? | -- | Repair complete |
