Circuit Description
The powertrain control module (PCM) uses the manifold absolute pressure (MAP) sensor to control fuel delivery and ignition timing. The MAP sensor measures the changes in the intake manifold pressure which results from engine load (intake manifold vacuum) and RPM changes; and converts these into a voltage output. The PCM sends a 5-volt reference voltage to the MAP sensor. As the manifold pressure changes, the output voltage of the sensor also changes. By monitoring the sensor output voltage, the PCM knows the manifold pressure. A lower pressure, low voltage, output voltage will be about 1 to 1.5 volts at idle. While higher pressure, high voltage, output voltage will be about 4.5 to 4.8 at wide open throttle (WOT). The MAP sensor is also used, under certain conditions, to measure barometric pressure, allowing the PCM to make adjustments for different altitudes.
Conditions for Setting
| • | MAP is greater than 82 kPa. |
| • | Throttle position (TP) is less than 12 percent. |
| • | Vehicle speed is less than 1 mph. |
| • | Above conditions are met for 10 seconds. |
| • | Engine has run for at least 20-40 seconds. |
| • | DTCs P0122 and P0123 are not set. |
Action Taken
The malfunction indicator lamp (MIL) illuminates. The PCM will substitute a fixed MAP value and use TP to control fuel delivery. The scan tool will not show defaulted value.
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after passing three consecutive diagnostic tests. |
| • | A history DTC will clear after 40 consecutive ignition cycles have occurred without a fault. |
| • | History and current DTCs can be cleared by using a scan tool. |
Diagnostic Aids
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 PCM as an indication of vehicle 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. Reading should be the same ±0.4 volt.
Inspect the CKT 416 to the IP junction connector terminal Ha for a short to voltage.
If a DTC P0107 is intermittent, refer to Symptoms Section 6E3-B or to Chart C-1D in Section 6E3-C1 for further diagnosis.
Important:
• After repairs use scan tool Fuel Trim Reset function to reset long term
fuel trim to 128. • If misfire is present, repair the cause of the misfire before using this
chart. The misfire counters may be used to determine which cylinders are misfiring.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step will determine if DTC P0108 is the result of a hard failure or an intermittent condition.
-
This step simulates conditions for a DTC P0107. If the PCM recognizes the change, the PCM and CKT 416 and CKT 432 are OK.
-
This step looks for an open CKT 469. If the circuit was open, a DTC P0118, P0530, and P0713 will also be set. If no other DTCs are set and the circuit is found to be open, then the open must be on the MAP sensor side of the sensor ground splice.
-
When CKT 432 is shorted to voltage, the TP will be displayed above 0 percent at all times and A/C High Side will be displayed high. The vehicle will also remain in Open Loop.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Was the On-Board Diagnostic (OBD) System Check perform? | -- | Go to Step 2 | |
Does the scan tool display a MAP voltage of the specified value or more? | 4 V | Go to Step 3 | Go to Step 4 | |
Does the scan tool display a MAP voltage of the specified voltage or less? | 1 V | Go to Step 5 | Go to Step 6 | |
4 |
Does the scan tool display a MAP voltage of the specified value or more? | 4 V | Go to Step 3 | Go to Diagnostic Aids |
Probe the MAP sensor ground circuit with a test light connected to battery voltage. Does the test light illuminate? | -- | Go to Step 7 | Go to Step 9 | |
Check the MAP signal circuit for a short to voltage or to the 5-volt reference circuit. Was a problem found? | -- | Go to Step 10 | Go to Step 11 | |
7 | Check the MAP sensor vacuum hose for being plugged or leaking. Was a problem found? | -- | Go to Step 8 | Go to Step 12 |
8 | Repair the vacuum hose as necessary. Is the action complete? | -- | -- | |
9 | Repair the open MAP sensor ground circuit. Is the action complete? | -- | -- | |
10 | Repair the MAP signal circuit Is the action complete? | -- | -- | |
11 | Replace the PCM. Is the action complete? | -- | -- | |
12 | Replace the MAP sensor. Is the action complete? | -- | -- | |
