Circuit Description
The throttle position (TP) sensor is a potentiometer. The gasoline Control Module (VCM / PCM or ECM) supplies about 5 volts on the TP sensor reference voltage circuit. The gasoline Control Module also supplies a ground circuit to the TP sensor. When the throttle is depressed, the TP signal voltage rises to near the supplied 5 volts. As the throttle is released, the TP signal voltage drops to around 0.6 volts. The gasoline Control Module and the Alternative Fuels ECM monitor the TP signal circuit voltage and determine the angle or opening of the throttle blade.
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 AF 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 (WOT).
This DTC is used to indicate a MAP sensor signal voltage that does not change when TP sensor voltage changes.
Conditions for Running the DTC
| • | The engine is operating on alternative fuel. |
| • | The engine has been operating for greater than 5 seconds. |
| • | No AF ECM DTCs are set. DTCs P1215, P1432, and P1433 may be set. |
| • | The TP sensor angle is less than 70 percent. |
Conditions for Setting the DTC
The AF ECM monitors that the MAP sensor pressure changes less than 6 kPa when the TP sensor angle changes by greater than 20 percent.
Action Taken When the DTC Sets
| • | The Alternative Fuels ECM will illuminate the MIL and store the DTC as History during 1 drive trip in which 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 tests the MAP sensors ability to correctly indicate BARO.
In order to determine the correct MAP sensor display of BARO for any elevation, perform either of the following:
-
This step tests the MAP sensors ability to correctly indicate engine vacuum.
-
This step indicates this sensor is currently functioning correctly. If you were sent to this diagnostic procedure from other service information return to that procedure now.
| • | Compare the recorded MAP sensor display value to the BARO display on a known good vehicle. |
| • | or |
| • | Obtain the local weather service barometer reading (in Hg). Multiply the barometer reading by 3.4 . The result indicates the correct BARO value for your area. |
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) |
Is the value greater than the value shown? | 75 kPa@altitude 95 kPa@sea level | Go to Step 3 | Go to Step 8 | |
Each one inch of vacuum should result in a 3 to 4 kPa drop in the MAP sensor display. Observe the Map sensor display for a skip or jump while increasing vacuum up to 20 inch Hg. Did you observe a skip or jump? | -- | Go to Step 8 | Go to Step 4 | |
4 | Observe the MAP sensor kPa display with 20 inch Hg. of vacuum applied to the MAP sensor. Is the value less than the value shown? | 34 kPa | Go to Step 5 | Go to Step 8 |
5 | Disconnect the MAP sensor from the J 23738-A . The MAP sensor display should return to the value recorded in step 2. Does the MAP sensor display return to the recorded value? | -- | Go to Step 6 | Go to Step 8 |
6 |
The TP Sensor should equal the first value or less. The TP Sensor should equal the second value or greater. Does the TP Sensor display indicate the values as expected? | 2% 98% | Go to Step 7 | Go to DTC P0121 |
The fault is not present. Refer to Diagnostic Aids. Are any DTCs stored that have not been diagnosed? | -- | Go to Intermittent Conditions | ||
8 |
Did you find a problem? | -- | Go to Step 9 | Go to Step 10 |
9 | Repair the connections or circuit as necessary. Refer to Wiring Repairs in Wiring Systems section of the G Van Service Manual. Is the action complete? | -- | Go to Step 11 | -- |
10 | Replace the MAP sensor. Refer to Manifold Absolute Pressure Sensor Replacement in the Engine Controls section of the G Van Service Manual. Is the action complete? | -- | Go to Step 11 | -- |
11 |
Does the scan tool indicate the diagnostic passed? | -- | System OK | Go to Step 2 |
