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 less than 14 kPa. |
| • | Engine speed is less than 1,200 RPM. |
| • | Throttle position (TP) is greater than 15.2 percent. |
| • | Above conditions are met for 0.2 second. |
| • | DTCs P0122 or 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 ground.
If a DTC P0107 is intermittent, refer to the Symptoms Section 6E3-B or to Chart C-1D in Section 6E3-C1 for further diagnosis.
Important: After repairs use the scan tool Fuel Trim Reset function to reset long term fuel trim to 128.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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This step determines if DTC P0107 is the result of a hard failure or an intermittent condition.
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Jumpering harness terminals B to C, signal circuit to 5 volts, will determine if the sensor is at fault or if there is a problem with the PCM or wiring.
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The scan tool may not display 5 volts. The important thing is that the PCM recognizes the voltage as more than 4 volts, indicating that the PCM and CKT 432 are OK.
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An open or short to ground in CKT 416 could also set a DTC P0122, P0530, and P1441.
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 below the specified value? | 0.25 V | Go to Step 3 | Go to Step 4 | |
Does the MAP voltage read more than the specified value? | 4.74 V | Go to Step 5 | Go to Step 6 | |
4 |
Does the scan tool display MAP voltage below the specified value? | 0.25 V | Go to Step 3 | Go to Diagnostic Aids |
5 | Inspect the electrical connector terminals for poor connections, proper contact tension or poor terminal to wire connection. Was a problem found? | -- | Go to Step 8 | Go to Step 9 |
Does the scan tool read over the specified value? | 4 V | Go to Step 7 | Go to Step 12 | |
Check the 5-volt reference circuit for an open or short to ground. Was a problem found? | -- | Go to Step 10 | Go to Step 11 | |
8 | Repair the connector terminals as necessary. Is the action complete? | -- | -- | |
9 | Replace the MAP sensor. Is the action complete? | -- | -- | |
10 | Repair the 5-volt reference circuit. Is the action complete? | -- | -- | |
11 | Replace the PCM. Is the action complete? | -- | -- | |
12 | Check the signal circuit for an open, short to ground, or short to sensor ground. Was a problem found? | -- | Go to Step 13 | Go to Step 11 |
13 | Repair the signal circuit. Is the action complete? | -- | -- | |
