Circuit Description
The brake pedal position (BPP) sensor provides an analog pedal position signal. Its output is hardwired to the electro-hydraulic power steering (EHPS) connector. The signal must be digitized and differentiated within the EHPS module to provide the necessary pedal rate signal.
The BPP sensor is a resistive sensor with a total resistance between 3 k - 5 k ohms with a maximum current draw of less than 16 ma. The BPP sensor will output an analog signal that is referenced to 5 volt which may increase or decrease monotonically with brake pedal depression. The sensor analog output shall have a specified electrical output over a mechanical range of 32 degrees rotation of the brake pedal pivot. Out-of-range values will be provided outside of the 32 degrees range. The EHPS module monitors the brake pedal position information from the BPP sensor every 5 milliseconds (200 Hz) for proper operation.
The BPP sensor contains the following three circuits:
| • | 5-volts reference circuit |
| • | Signal circuit |
| • | Low reference circuit |
The EHPS excites the BPP sensor with the 5-volt reference and can determine the brake pedal position by reading the signal circuit output. The brake pedal travel is physically constrained to only use a portion of the BPP sensor. A portion of the BPP sensor is reserved for circuit low and circuit high guard bands. This diagnostic, DTC C0284, is used to determine if the sensor output reports a voltage in the high guard band.
Conditions for Running the DTC
| • | EHPS module in RUN mode. |
| • | Ignition switch in ACC or ON position |
| • | Battery voltage is between 12 - 58 volts. |
Conditions for Setting the DTC
| • | Output voltage ratio sensed by the EHPS module is less than 98.44 percent of the excitation voltage (voltage over limit). |
| • | BPP sensor fork is off of brake pedal pin. |
Action Taken When the DTC Sets
| • | System operation is reduced. |
| • | The SERVICE BRAKE SYSTEM message will be displayed. |
| • | Ramp the motor speed input to the commanded flow resolved from a default brake pedal position. |
| • | Stores a DTC C0284 in the powertrain control module (PCM). |
| • | History DTC C0284 will be set in PCM. |
Conditions for Clearing the DTC
| • | Output voltage ratio sensed by the EHPS module drops below 98.44 percent of the excitation voltage. |
| • | Using the scan tool. |
| • | A history DTC will clear after 255 consecutive ignition cycles if the condition for the malfunction is no longer present. |
Diagnostic Aids
It may be necessary to check Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
Checks the Input Voltage data parameter.
-
Checks the Output Voltage data parameter.
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Tests for an open or short to voltage in the BPP sensor 5 volt supply circuit.
-
Tests for an open or short to voltage in the BPP sensor 5 volt return circuit.
-
Tests for a short to voltage in the BPP sensor signal circuit.
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Power Steering Schematics Connector End Views Reference: Power Steering Connector End Views | |||
1 | Did you perform the electro-hydraulic power steering (EHPS) Diagnostic System Check? | Go to Step 2 | |
|
Important: Ensure that the fork of the brake pedal position (BPP) sensor is properly aligned on the pin attached to the brake pedal.
Does the input voltage reading increase as the brake pedal is depressed? | Go to Step 3 | Go to Step 4 | |
With a scan tool, observe the BPP sensor Output Volts parameter, while pressing down on the brake pedal. Does the output voltage reading decrease as the brake pedal is depressed? | Go to Step 6 | Go to Step 5 | |
Test the BPP sensor 5 volt supply circuit for an open or short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 11 | Go to Step 7 | |
Test the BPP sensor 5 volt return circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 11 | Go to Step 8 | |
Test the BPP sensor signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 11 | Go to Step 9 | |
7 | Inspect for poor connections at the harness connector of the BPP sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 11 | Go to Step 9 |
8 | Inspect for poor connections at the harness connector of the EHPS module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 11 | Go to Step 10 |
9 |
Important: Always perform the calibration procedure for the BPP sensor. Refer to Brake Pedal Position Sensor Calibration Description and Operation . Replace the BPP sensor. Refer to Brake Pedal Position Sensor Replacement . Did you complete the replacement? | Go to Step 11 | -- |
10 |
Important: Always perform the calibration procedure for the BPP sensor. Refer to Brake Pedal Position Sensor Calibration Description and Operation . Replace the EHPS powerpack. Refer to Power Steering Pump Replacement . Did you complete the replacement? | Go to Step 11 | -- |
11 |
Does the DTC reset? | Go to Step 2 | System OK |
