Circuit Description
The Manifold Absolute Pressure (MAP) sensor is a pressure sensor. The gasoline control module (VCM / PCM or ECM) supplies about 5 volts on the MAP sensor reference voltage circuit. The gasoline control module also supplies a ground circuit to the MAP sensor. When manifold vacuum is low, the MAP signal voltage rises to near 4.5 volts. As manifold vacuum increases, the MAP signal voltage drops to around 1.0 volt. The gasoline control module and the AF ECU, monitor the MAP signal circuit voltage and determine the vacuum within the intake manifold.
Certain vehicle models will also use the MAP sensor in order to determine the barometric pressure when the ignition switch is turned ON and the engine is NOT cranked. This BARO reading may also be updated whenever the engine is operated at Wide Open Throttle.
This DTC is used to indicate a MAP sensor signal voltage that is below the normal operating range of the sensor.
Conditions for Running the DTC
| • | The engine is operating on alternative fuel. |
| • | The engine speed is more than 500 RPM. |
| • | DTCs P0121, P0122, or P0123 are not set. |
| • | The TP angle is less than 4 percent when the engine speed is less than 1200 RPM. |
| OR |
| The TP angle is more than 20 percent when the engine speed is more than 1300 RPM. |
Conditions for Setting the DTC
The AF ECU monitors a MAP sensor signal voltage of less than 0.098 volts for at least 4 seconds continuously.
Action Taken When the DTC Sets
| • | A first failure of this DTC will NOT illuminate the MIL and will store as Last Test Failed but not as History. |
| • | The AF ECU will illuminate the MIL and store the DTC as History after TWO consecutive drive trips that the diagnostic runs and fails. |
| • | The AF ECU will record operating conditions at the time the DTC sets. This information will be stored as Freeze Frame data. |
Conditions for Clearing the MIL/DTC
| • | The Last Test Failed status will clear when the DTC runs and passes. |
| • | The AF ECU will turn OFF the MIL after 3 consecutive drive trips that the DTC runs and passes. |
| • | The History status will clear after 40 consecutive WARM-UP cycles with NO failures of ANY DTC. |
| • | All DTC Information can be cleared using a scan tool. |
| • | Interruption of Control Module (AF ECU / VCM / PCM or ECM) power or ground MAY clear DTC Information. Clearing DTC Information with this method is inconsistent and should not be performed. |
Diagnostic Aids
Fault Not Present
Fault Not Present indicates the condition that caused the DTC to set is intermittent and not currently present. Refer to Intermittent Conditions for additional information. If any additional DTCs were stored proceed to the applicable DTC table in the order stated in the OBD System Check.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step determines if the failure condition affects the gasoline control module.
-
This step determines if the failure condition is present.
-
This step determines if the MAP sensor is the cause of the condition.
-
This step determines if the 5 volt reference circuit is the cause of the condition. 4.8 volts is the minimum output that the gasoline control module should supply on the 5 volt reference circuit.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the AF Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Alternative Fuels (AF) Powertrain On Board (OBD) System Check | |
Important: The VCM MAP sensor data parameter is active only while the engine is running. Is the MAP voltage less than the specified value? | 0.20 V | |||
Is the MAP voltage less than the specified value? | 0.09 V | |||
4 | The fault is not present. Refer to Diagnostic Aids. Are any DTCs stored that have not been diagnosed? | -- | Go to Intermittent Conditions | |
Important: The VCM MAP sensor data parameter is active only while the engine is running. Is the MAP voltage more than the specified value? | 4.8 V | |||
Is the voltage less than the specified value? | 4.8 V | |||
7 |
Was a wiring or terminal repair necessary? | -- | ||
8 |
Was a wiring repair made? | -- | ||
9 |
Was a wiring or terminal repair necessary? | -- | ||
10 |
The 5 volt reference circuits (A and B) are shared within the VCM. The short may be located on either of the 5 volt reference circuits that the VCM provides. Disconnect the AF ECU connector that contains the 5 volt reference circuit in order to determine if the AF ECU is the cause of the short. Disconnect the other sensors that are connected to the gasoline control module 5 volt reference circuits in order to determine if a sensor is the cause of the short. Was a repair made? | -- | ||
11 | Replace the MAP sensor. Refer to Manifold Absolute Pressure Sensor Replacement Is the replacement complete? | -- | -- | |
12 |
Important: The following control module replacement procedures must all be completed before attempting to operate the vehicle.
Important: In order to perform the variation learn procedure a switch-over to gasoline operation is necessary. Remove the CNG 20 amp fuse in order to perform the switch-over. All of the above procedures are located in the gasoline service manual. Is the replacement complete? | -- | -- | |
13 | Replace the AF ECU. Refer Engine Control Unit Replacement . Is the replacement complete? | -- | -- | |
14 |
Did this DTC RUN and PASS? | -- | System OK |
