Description
The barometric pressure sensor and circuitry are located inside of the powertrain control module. The powertrain control module uses barometric pressure information in order to compensate for altitude changes. The barometric pressure sensor reading is displayed on a scan tool when the ignition switch is ON and the engine is OFF.
Conditions for Setting the DTC
The PCM performs a comparison with the MAP sensor checking for the following:
| • | Difference between barometric pressure and manifold absolute pressure is 67 kPa or more. |
| • | CTP switch ON. |
| • | Engine speed is greater than 2000 RPM. |
| • | The above conditions are met for 5 seconds or more. |
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) after two consecutive ignition cycles in which the diagnostic runs with the fault active. |
| • | The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer. |
Conditions for Clearing the MIL/DTC
| • | The MIL turns OFF after three consecutively passing trips without a fault present. |
| • | A History DTC clears after 40 consecutive warm-up cycles without a fault. |
| • | Use the scan tool Clear DTC Information function or disconnect the PCM battery feed in order to clear the DTC. |
Diagnostic Aids
A malfunctioning or skewed MAP sensor may cause a DTC P1451 to set.
Barometric pressure varies depending on the weather conditions and the altitude.
If a DTC P1451 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set.
Test Description
The numbers below refer to the step numbers in the Diagnostic Table.
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The Powertrain (OBD) System Check 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.
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This step checks for a MAP sensor fault.
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This step determines if the fault is present.
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This step checks that the MAP sensor is reading atmospheric pressure. Normal atmospheric pressure will be near 100 kPa at sea level. When the engine is not running intake manifold pressure and atmospheric pressure should be the same.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | |||
Check for a MAP sensor DTC P1408. Is a DTC P1408 set? | -- | Go to the Applicable DTC Table | ||
Is DTC P1451 set? | -- | Go to Diagnostic Aids | ||
Is the MAP sensor display (barometric pressure reading) at approximately the specified value? | 100 kPa | Go to Diagnostic Aids | ||
5 | Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | -- | |
6 |
Are any DTCs displayed on the scan tool? | -- | Go to the Applicable DTC Table | System OK |
