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 the manifold vacuum is low, the MAP signal voltage rises to near 4.5 volts. As the manifold vacuum increases, the MAP signal voltage drops to around 1 volt. The gasoline Control Module and the Alternative Fuel ECM 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 (BARO) 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 above the normal operating range of the sensor.
Conditions for Running the DTC
| • | The engine is operating on alternative fuel. |
| • | The engine speed is greater than 500 RPM. |
| • | DTCs P0121, P0122, or P0123 are not set. |
| • | The TP angle is less than 4 percent. |
Conditions for Setting the DTC
The Alternative Fuel ECM monitors a MAP sensor signal voltage of greater than 4.8 volts for at least 4 seconds continuously.
Action Taken When the DTC Sets
| • | The Alternative Fuel ECM will switch-over to gasoline fuel operation. |
| • | The Alternative Fuel ECM will not attempt alternative fuel operation until the next key cycle. |
| • | A first failure of this DTC will NOT illuminate the MIL and will store as Last Test Failed but not as History. |
| • | The Alternative Fuels ECM will illuminate the MIL and store the DTC as History after 2 consecutive drive trips that the diagnostic runs and fails. |
| • | The Alternative Fuels ECM 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 Alternative Fuels ECM 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 with a scan tool. |
Diagnostic Aids
Intermittent Condition
A fault not present indicates the condition that caused the DTC to set is intermittent and not currently present. Refer to the Intermittent Conditions diagnostic information located in Symptoms - Engine Controls. If any additional DTCs were stored proceed to the applicable DTC table in the order stated in Diagnostic System Check - Alternative Fuels (Engine Controls) .
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 shorted condition.
-
This step determines if an open sensor ground condition is present.
-
This step determines if the 5-volt reference circuit is shorted to a voltage. 5.2 volts is the maximum output that the gasoline Control Module should supply on the 5-volt reference circuit.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Did you perform the Alternative Fuels Engine Controls Diagnostic System Check? | -- | Go to Step 2 | Go to Diagnostic System Check - Alternative Fuels (Engine Controls) |
Does the MAP sensor data parameter indicate MAP voltage greater than the specified value? | 4.8 V | Go to Step 5 | Go to Step 3 | |
Does the MAP sensor data parameter indicate MAP voltage greater than the specified value? | 4.8 V | Go to Step 11 | Go to Step 4 | |
4 | The fault is not present. Refer to Diagnostic Aids. Are any DTCs stored that have not been diagnosed? | -- | Go to Intermittent Conditions | |
Does the MAP sensor data parameter indicate MAP voltage LESS than the specified value? | 0.25 V | Go to Step 6 | Go to Step 10 | |
Connect the J 35616-200 Unpowered Test Lamp between the sensor ground circuit terminal and BATTERY POSITIVE. Is the test lamp illuminated? | -- | Go to Step 7 | Go to Step 9 | |
Is the voltage less than the voltage specified? | 5.2 V | Go to Step 14 | Go to Step 8 | |
8 |
Some 5-volt reference circuits are shared within the PCM. The short may be located on either of the 5-volt reference circuits that the PCM provides. Was a wiring repair made? | -- | Go to Step 17 | Go to Step 15 |
9 |
Was a wiring or terminal repair necessary? | -- | Go to Step 17 | Go to Step 15 |
10 |
Disconnect the Alternative Fuel ECM connector that contains the MAP signal circuit in order to determine if the ECM is the cause of the short to voltage. Was a wiring repair made? | -- | Go to Step 17 | Go to Step 15 |
11 |
Is MAP signal circuit continuity indicated? | -- | Go to Step 13 | Go to Step 12 |
12 | Repair the open MAP signal circuit between the MAP signal circuit splice and the Alternative Fuel ECM. Is the circuit repair complete? | -- | Go to Step 17 | -- |
13 |
Was a terminal repair made? | -- | Go to Step 17 | Go to Step 16 |
14 | Replace the MAP Sensor. Refer to Manifold Absolute Pressure Sensor Replacement in the Engine Controls section of the G Van Service Manual. Is the replacement complete? | -- | Go to Step 17 | -- |
15 |
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 G Van Service Manual. Is the replacement complete? | -- | Go to Step 17 | -- |
16 |
Is the replacement complete? | -- | Go to Step 17 | -- |
17 |
Did this DTC run and pass? | -- | System OK | Go to Step 2 |
