Circuit Description
This diagnostic monitors the manifold absolute pressure (MAP) sensor response to pressure changes in the intake manifold. The pressure changes occur based on engine load and the throttle valve opening. The MAP sensor has the following circuits:
| • | A 5-volt reference circuit |
| • | A low reference circuit |
| • | A signal circuit |
The powertrain control module (PCM) supplies 5 volts to the MAP sensor on the 5-volt reference circuit. The PCM also provides a ground on the low reference circuit. The PCM receives a low voltage on the signal circuit when manifold vacuum is high at idle or deceleration. The PCM receives a high voltage when manifold vacuum is low at wide open throttle (WOT) or when the ignition is ON and the engine is OFF. If the PCM detects a MAP sensor signal for voltage that is more than a predetermined value, this DTC sets.
The following table illustrates the difference between MAP kPa, signal voltage, and engine vacuum.
Engine Condition | MAP kPa | MAP Signal Voltage | Manifold Vacuum |
|---|---|---|---|
Idle | Low | Low | High |
Deceleration | Low | Low | High |
Ignition ON, Engine OFF | High | High | Zero |
Wide-Open Throttle | High | High | Low |
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0108 Manifold Absolute Pressure (MAP) Sensor Circuit High Voltage
Conditions for Running the DTC
| • | The engine is operating. |
| • | DTC P0107 is not set. |
| • | DTC P0108 runs continuously once the above conditions are met. |
Conditions for Setting the DTC
The MAP sensor signal is 4.49 volts or more for at least 2 seconds.
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails. |
| • | The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Freeze Frame/Failure Records. |
| • | The PCM enters the Fail Safe Function and uses default MAP values based on throttle position, while the fuel control system operates in OPEN LOOP. |
Conditions for Clearing the MIL/DTC
| • | The MIL turns OFF after 3 consecutively passing trips without a fault present. |
| • | A history DTC clears after 40 consecutive warm-up cycles without a fault. |
| • | Perform the scan tool Clear DTC Information function. |
Diagnostic Aids
| • | Inspect for the following conditions: |
| - | Inspect for an exhaust gas recirculation (EGR) valve that is stuck open. |
| - | Inspect for a restricted exhaust system. Refer to Restricted Exhaust . |
| • | An intermittent malfunction may be caused by a fault in the MAP sensor circuit. Inspect the wiring harness and the components for an intermittent condition. Refer to Intermittent Conditions . |
| • | If the DTC P0108 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC was first set. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
The Diagnostic System Check - Vehicle prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
-
This step determines if a MAP sensor malfunction is present. The input signal of the MAP sensor should indicate atmospheric pressure with the ignition ON, engine OFF. The MAP sensor will vary with atmospheric pressure. A typical pressure at sea level is 100 kPa (29-30 in Hg).
-
The MAP sensor signal circuit carries a 5 volt bias that can be measured with the DMM. If the measured voltage is near zero there is an open or a faulty PCM.
-
This step checks for an open in the MAP sensor ground circuit.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views | ||||
Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | ||
Is the MAP sensor value within the specified range? | 95-100 kPa | Go to Step 3 | Go to Step 4 | |
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Diagnostic Aids |
4 | Was DTC P0502 also set? | -- | Go to Step 9 | Go to Step 5 |
Is the voltage near the specified value? | 4.9 V | Go to Step 7 | Go to Step 6 | |
6 |
Was a repair necessary? | -- | Go to Step 12 | Go to Step 11 |
Probe the MAP sensor ground circuit on the harness side with a test lamp connected to B+. Does the test lamp illuminate? | -- | Go to Step 10 | Go to Step 8 | |
8 | Repair the open in the sensor ground circuit between the MAP sensor and S115. Refer to Wiring Repairs . Is the action complete? | -- | Go to Step 12 | -- |
9 | Repair the open in the sensor ground circuit between the powertrain control module (PCM) and S115. Refer to Wiring Repairs . Is the action complete? | -- | Go to Step 12 | -- |
10 | Replace the MAP sensor. Refer to Manifold Absolute Pressure Sensor Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- |
11 |
Did you complete the replacement? | -- | Go to Step 12 | -- |
12 |
Does the DTC run and pass? | -- | Go to Step 13 | Go to Step 2 |
13 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |
