For 1990-2009 cars

### Circuit Description

The DTC P1408 Manifold Absolute Pressure (MAP) Sensor Circuit diagnostic monitors the operation of the MAP sensor. The MAP sensor measures the change in intake manifold pressure (vacuum). The powertrain control module (PCM) provides a 5 volt reference signal to the MAP sensor. The change in the pressure that results from engine load and RPM changes is converted into a voltage signal that is monitored by the PCM. By monitoring the sensor output voltage, the PCM can detect a change in manifold pressure.

### Condition for Running the DTC

• | The ignition is ON or the engine is running.

• | The engine coolant temperature is more than 45°C (113°F).

• | The intake air temperature is more than 5°C (41°F).

• | The throttle position is less than 10 degrees.

### Conditions for Setting the DTC

The signal voltage is more than 4.8 volts when the throttle position is less than 10 degrees.

OR

The signal voltage is less than 0.2 volts when the throttle position is more than 5 degrees.

### Action Taken When the DTC Sets

• | The malfunction indicator lamp (MIL) will illuminate after two consecutive ignition cycles in which the diagnostic runs with the fault active.

• | The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame buffer.

### Conditions for Clearing the MIL/DTC

• | The MIL will turn OFF after three consecutive drive cycles without a fault present.

• | A DTC will clear after 40 consecutive warm-up cycles without a fault.

• | The DTCs can be cleared by using a scan tool or by disconnecting the PCM battery feed.

### Diagnostic Aids

Check for a steady and accurate supply of manifold vacuum to the MAP sensor.

An intermittent malfunction may be caused by a fault in the MAP sensor circuit. Inspect the wiring harness and components for an intermittent condition. Refer to Intermittent Conditions .

If the DTC P1408 is intermittent, driving the vehicle under the following conditions can verify whether the fault is present. Perform the scan tool Clear DTC Information function. Road test the vehicle while monitoring the DTC P1408 diagnostic on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If a DTC P1408 appears in the Not Ran Since Code Cleared list, the P1408 diagnostic has not yet run. When the DTC P1408 does not appear in the Not Ran Since Code Cleared list, the P1408 diagnostic has run. If the MIL is NOT ILLUMINATED, and there is no PENDING DTC Status in DTC Information, the P1408 diagnostic has passed. DTCs MUST BE CLEARED in order to view the CURRENT STATUS of the Not Ran Since Code Cleared list. DO NOT FORGET that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for CURRENT or PENDING status, in order to determine the outcome of the diagnostic test involved.

If the DTC P1408 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions since the DTC was first set.

### Test Description

The numbers below refer to the step numbers in the diagnostic table.

1. The Diagnostic System Check-Engine Controls 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.

2. Review the Freeze Frame data to determine when the DTC set. Always record this information.

3. This step checks the MAP sensor calibration.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Engine Controls Schematics
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | Go to Diagnostic System Check - Engine Controls
2 |

1. Start the engine.
2. Idle the engine at operating temperature.
3. Measure the voltage by backprobing the MAP sensor signal (input) circuit at the PCM, using a DMM.

Is the voltage within the specified value?

0.2 to 4.6 V

Go to Step 3

Go to Step 4

3 |

1. Turn ON the ignition, leaving the engine OFF.
2. Clear the scan tool data information.
3. Operate the vehicle within the Freeze Frame conditions as specified.

Is a DTC P1408 set?

--

Go to Step 4

Go to Diagnostic Aids

4 |

1. Turn OFF the ignition.
2. Disconnect the MAP sensor.
3. Turn ON the ignition, leaving the engine OFF.
4. Measure the voltage from the MAP sensor reference circuit using the DMM.

Is the voltage at the specified value?

5 V

Go to Step 5

Go to Step 8

5 | Probe the MAP sensor ground circuit with a test lamp connected to B+. Did the test lamp illuminate? | -- | Go to Step 6 | Go to Step 9
6 |

1. Check the MAP sensor signal (input) circuit for an open or a short between the MAP sensor and the PCM.
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 12

Go to Step 7

7 |

1. Turn OFF the ignition.
2. Reconnect the MAP sensor electrical connector.
3. Turn ON the ignition, leaving the engine OFF.
4. Measure the voltage while backprobing the MAP sensor signal (input) circuit at the PCM using the DMM.
5. Apply a small vacuum to the pressure passage of the sensor using a hand vacuum pump.

Did the voltage drop when the vacuum was applied?

--

Go to Step 11

Go to Step 10

8 |

1. Check for an open or a short in the 5 volt reference circuit between the MAP sensor and the PCM.
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 12

Go to Step 11

9 |

1. Check for an open or a faulty connection in the ground circuit between the MAP sensor and the PCM.
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 12

Go to Step 11

10 | Replace the MAP sensor. Refer to Manifold Absolute Pressure Sensor Replacement . Is the action complete? | -- | Go to Step 12 | --
11 | Replace the PCM. Refer to Powertrain Control Module Replacement . Is the replacement complete? | -- | Go to Step 12 | --
12 |

1. Use the scan tool in order to clear the DTCs.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC run and pass?

--

Go to Step 13

Go to Step 2

13 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List | System OK