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
| • | Engine speed is stable ±150 RPM. |
| • | Idle air control (IAC) is stable ±10 counts. |
| • | Throttle position (TP) is stable ±1 percent. |
| • | Above conditions are met for 0.4 second. |
| • | MAP changes more than 6.3 kPa in 15.6 milliseconds. |
| • | DTCs P0107, P0108, 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 or ground.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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Output changes more than 6.3 kPa verify if the fault is present now.
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This step simulates DTC Pie. If the PCM recognizes the change, the PCM and CKT 416 and CKT 432 are OK. If CKT 469 is faulty, the A/C system may also be inoperative and a DTC Pie may also be set.
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Output changes greater than 6.3 kPa indicate a possible faulty connector or connection, a cracked vacuum hose or faulty sensor that is internally affected from the twisting motion of this step.
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Check terminals for being backed out, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wiring connections or physical damage to the wiring harness.
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Because the MAP sensor is very sensitive to pressure change, it must have its own vacuum source or it may detect pressure changes due to other devices using the same source.
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 kPa varying more than the specified value? | 6.3 kPa | Go to Step 3 | Go to Step 4 | |
Does the scan tool display a steady MAP voltage of the specified voltage or less? | 1 V | Go to Step 5 | Go to Step 6 | |
With the engine still idling, twist the MAP sensor electrical connector by hand. Does the scan tool display a MAP kPa varying more than the specified value? | 6.3 kPa | Go to Step 3 | Go to Step 7 | |
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 | |
6 | Inspect the PCM electrical connector terminals for poor connection, proper contact tension or poor terminal to wire connection. Was a problem found? | -- | Go to Step 8 | Go to Step 12 |
7 |
Does the scan tool display a MAP kPa varying more than the specified value? | 6.3 kPa | Go to Step 3 | Go to Diagnostic Aids |
8 | Repair the connector terminals as necessary. Is the action complete? | -- | -- | |
Is the vacuum source OK? | -- | Go to Step 10 | Go to Step 11 | |
10 | Replace the MAP sensor. Is the action complete? | -- | -- | |
11 | Repair vacuum source. Is the action complete? | -- | -- | |
12 | Replace the PCM. Is the action complete? | -- | -- | |
