Circuit Description
The vehicle speed sensor (VSS) assembly provides vehicle speed information to the powertrain control module (PCM). The VSS assembly is a permanent magnet (PM) generator. The PM generator produces a pulsing AC voltage as the speed sensor rotor teeth on the transmission governor assembly pass through the sensor's magnetic field. The AC voltage level and the number of pulses increases as the speed of the vehicle increases. The output voltage varies from a minimum of 0.5 volts AC at 25 RPM to more than 100 volts at 200 RPM. The PCM converts the pulsing voltage to vehicle speed. The PCM uses the vehicle speed signal to calculate torque converter clutch (TCC) scheduling.
When the PCM detects a low vehicle speed and there is a high engine speed in a drive range, then DTC P0502 sets. DTC P0502 is a type B DTC.
Conditions for Running the DTC
| • | No MAP DTCs P0107 or P0108 |
| • | No TP DTCs P0122 or P0123 |
| • | The TP angle is greater than 15%. |
| • | MAP is greater than 50 kPa. |
| • | The transmission is in a drive range. |
| • | All of the above conditions are met for 3 seconds. |
Conditions for Setting the DTC
DTC P0502 sets during the second consecutive trip in which the following condition occurs:
The vehicle speed is less than 3.2 km/h (2 mph).
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL). |
| • | TCC will not apply. |
| • | DTC P0502 stores in PCM history. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns OFF the MIL during the third consecutive trip in which the diagnostic test runs and passes. |
| • | A scan tool clears the DTC from the PCM history. |
| • | The PCM clears the DTC from PCM history if the vehicle completes 40 consecutive warm-up cycles without an emission related fault occurring. |
Diagnostic Aids
| • | Inspect for electromagnetic interferences (EMI) induced on circuit 400 and circuit 401 by an improperly routed harness. |
| • | Inspect the wiring at the PCM, the vehicle speed sensor (VSS) assembly connector and all other circuit connecting points for the following conditions: |
| - | A backed out terminal |
| - | A damaged terminal |
| - | Reduced terminal tension |
| - | A chafed wire |
| - | A broken wire inside the insulation |
| - | Moisture intrusion |
| - | Corrosion |
| • | When diagnosing for an intermittent short or open condition, massage the wiring harness while watching the test equipment for a change. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step tests for a vehicle speed signal.
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This step checks for the VSS assembly ability to produce an AC voltage.
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This step checks for correct circuit resistance.
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When the VSS assembly is disconnected, the circuit resistance should be infinite.
-
This step checks for improper voltage in the circuit.
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This step inspects for possible mechanical problems.
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Replace the PCM only after you have completed the preceding diagnostic steps.
Step | Action | Value(s) | Yes | No | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Were you sent here from the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||||||||
Important: Before clearing the DTCs, use the scan tool in order to record the Freeze Frame and Failure Records. Using the Clear Info function erases the Freeze Frame and Failure Records from the PCM. Notice: Support the lower control arms in the normal horizontal position in order to avoid damage to the drive axles. Do not operate the vehicle in gear with the wheels hanging down at full travel. With the drive wheels rotating, does the transmission output speed increase when the wheel speed increases? | -- | Go to Diagnostic Aids | ||||||||||||
Can a voltage value greater than the specified amount be obtained? | 0.5V AC | |||||||||||||
Select ohms on the J 39200 DMM in order to measure circuit resistance. Is the circuit resistance within the specified range? | 139-376ohms | |||||||||||||
5 | Is the circuit resistance greater than the specified value? | 376 ohms | ||||||||||||
6 | Is the circuit resistance less than the specified value? | 139 ohms | -- | |||||||||||
Is the circuit resistance less than specified? | 139 ohms | |||||||||||||
8 | Inspect circuits 400 and 401 for being shorted together. Refer to General Electrical Diagnosis in Wiring Systems. Was the condition found? | -- | -- | |||||||||||
9 | Inspect circuit 400 for a short to ground. Refer to General Electrical Diagnosis in Wiring Systems. Was the condition found? | -- | ||||||||||||
Does the voltmeter display system voltage? | -- | |||||||||||||
11 | Inspect circuit 400 for a short to power. Refer to General Electrical Diagnosis in Wiring Systems. Was the condition found? | -- | -- | |||||||||||
12 | Inspect circuits 400 and 401 for an open. Refer to General Electrical Diagnosis in Wiring Systems. Was the condition found? | -- | ||||||||||||
13 | Repair circuits 400 and 401. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | -- | |||||||||||
14 | Repair circuits 400. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | -- | |||||||||||
Refer to Unit Repair. Is the repair or replacement complete? | -- | -- | ||||||||||||
16 | Replace the VSS assembly. Refer to Vehicle Speed Sensor Replacement . Is the replacement complete? | -- | -- | |||||||||||
Replace the PCM. Refer to PCM Replacement/Programming in Engine Controls. Is the replacement complete? | -- | -- | ||||||||||||
18 | Perform the following procedure in order to verify the repair:
Has the test run and passed? | -- | System OK |
