Circuit Description
The manifold absolute pressure (MAP) sensor is a pressure sensor. The powertrain control module (PCM) supplies about 5 volts on the MAP sensor reference voltage circuit. The PCM 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 PCM 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 sets when the MAP sensor signal voltage 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. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step determines if the condition is present.
-
This step determines if the condition affects the PCM.
-
This step determines if the MAP sensor is the shorted condition.
-
This step determines if an open sensor ground condition is present.
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This step determines if the 5-volt reference circuit is shorted to a voltage. 5.2 volts is the maximum output that the PCM should supply on the 5-volt reference circuit.
Step | Action | Value(s) | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||||||
1 | Did you perform the Diagnostic System Check Alternative Fuels - Engine Controls? | -- | Go to Step 2 | Go to Diagnostic System Check - Alternative Fuels (Engine Controls) | ||||
Does the DTC fail this ignition cycle? | -- | Go to Step 3 | Go to Intermittent Conditions | |||||
Does the MAP sensor data parameter indicate MAP voltage greater than the specified value? | 4.8 V | Go to Step 4 | Go to Step 12 | |||||
Does the MAP sensor data parameter indicate MAP voltage less than the specified value? | 0.25 V | Go to Step 5 | Go to Step 9 | |||||
Probe the ground circuit of the MAP sensor with a test lamp connected to battery positive. Does the test lamp illuminate? | -- | Go to Step 6 | Go to Step 8 | |||||
Measure the voltage on the 5-volt reference circuit with a DMM. Does the DMM display a voltage less than the specified value? | 5.2 V | Go to Step 10 | Go to Step 7 | |||||
7 |
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. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 11 | ||||
8 |
Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 11 | ||||
9 | Test the MAP signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the C/K Pickup Service Manual. 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. Did you find and correct the condition? | -- | Go to Step 14 | Go to Step 11 | ||||
10 | Replace the MAP Sensor. Refer to Manifold Absolute Pressure Sensor Replacement in Engine Controls in the C/K Pickup Service Manual. Did you complete the replacement? | -- | Go to Step 13 | -- | ||||
11 | Replace the PCM. Refer to Powertrain Control Module Programming in Engine Controls in the C/K Pickup Service Manual. Did you complete the replacement? | -- | Go to Step 13 | -- | ||||
12 | Replace the Alternative Fuel ECM. Refer to Alternative Fuels Engine Control Module Replacement . Did you complete the replacement? | -- | Go to Step 13 | -- | ||||
13 |
Does the DTC run and pass? | -- | Go to Step 14 | Go to Step 2 | ||||
14 | With a scan tool, select Capture Info in order to observe the stored information. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||
