Circuit Description
The manifold absolute pressure (MAP) sensor measures the changes in the intake manifold pressure which result from engine load, or the intake manifold vacuum, and RPM changes, and converts these into a voltage output. The Powertrain Control Module (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 calculates the manifold pressure. A lower pressure, low voltage, output voltage will be approximately 1.0 to 1.5 volts at idle. Higher pressure, high voltage, output voltage will be approximately 4.5 to 4.8 volts at wide open throttle (WOT). The MAP sensor is also used to measure barometric pressure, allowing the PCM to make adjustments for different altitudes. The PCM uses the MAP sensor to control fuel delivery and ignition timing.
Test Description
The number(s) below refer(s) to the step number(s) on the Diagnostic Table.
Important: Be sure to use the same diagnostic test equipment for all measurements.
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The Powertrain OBD System check prompts you to complete some of the basic checks and to store the Freeze Frame and Failure records data on the scan tool if applicable. This creates an electronic copy of the data captured when the fault occurred. The scan tool stores this data for later reference.
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Applying 34 kPa (10 in of Hg) vacuum to the MAP sensor should cause the voltage to be 1.5 to 2.1 volts less than the voltage at Step 3. Upon applying vacuum to the sensor, the change in the voltage should be instantaneous. A slow voltage change indicates a malfunctioning sensor.
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Check the vacuum hose to the sensor for leaking or restriction. Be sure that no other vacuum devices are connected to the MAP hose.
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Important: Make sure that the electrical connector remains securely fastened.
Move the sensor electrical connector by hand (only) while watching scan tool to check for an intermittent connection. Output that changes greater than 0.10 volt indicate a bad connection. If OK, replace the sensor.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
2 | Install a scan tool and check for any MAP Sensor DTCs. Were any MAP Sensor DTCs set? | -- | Go to MAP DTC Tables | |
3 |
Are the voltage readings between the 2 vehicles within the specified value? | ± 0.4 V | ||
Is the difference greater than the specified value? | 34 kPa (10 in of Hg) 1.5 V | |||
5 | Replace the MAP sensor. Is the action complete? | -- | -- | |
Check the MAP sensor vacuum source for leakage or for a restriction and be sure that the vacuum source supplies the MAP sensor only. Is the action complete? | -- | |||
Check the MAP sensor electrical connector terminals and repair the terminals as necessary. Was a repair necessary? | -- | |||
8 | Repair any leakage or restriction in the MAP sensor vacuum source. Is the action complete? | -- |
| |
9 | Operate the vehicle within the conditions under which the original symptom was observed. Does the system now operate properly? | -- | System OK |
