Circuit Description
The automatic transmission output shaft speed (AT OSS) sensor is a three-wire magnetic pick-up sensor that is mounted externally to the transmission. The OSS utilizes the gear teeth, located on the output shaft, to generate a voltage signal of varying frequency that corresponds to the rotational speed of the output shaft. The OSS signal is sent to the PCM and is used to calculate the vehicle speed. Simultaneously, the automatic transmission input shaft speed sensor (AT ISS) signal is used to calculate the vehicle speed. The PCM compares the vehicle speed calculated from both speed sensors and uses this comparison for diagnosis of the speed sensors.
If the PCM detects a low OSS calculated vehicle speed and a high ISS calculated vehicle speed for 10 seconds, DTC P0502 sets. DTC P0502 is a type A DTC.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0502 Vehicle Speed Sensor (VSS) Circuit Low Voltage
Conditions for Running the DTC
| • | No TR Switch DTCs P0705 or P0706. |
| • | No AT ISS DTCs P0716 or P0717. |
| • | No Clutch PC Solenoid 1 DTCs P0962 or P0963. |
| • | No Clutch PC Solenoid 2 DTCs P0966 or P0967. |
| • | No SS 1 DTCs P0973 or P0974. |
| • | No SS 2 DTCs P0976 or P0977. |
| • | No SS 3 DTCs P0979 or P0980. |
| • | No TCC PC Solenoid DTCs P2763 or P2764. |
| • | No TCC enable solenoid DTCs P2769 or P2770. |
| • | The ignition voltage is greater than 11 volts. |
| • | The engine speed is 500 RPM or greater. |
| • | The vehicle speed is greater than 20 km/h (13 mph). |
| • | The commanded gear is greater than 1st. |
| • | The selected range is D, I, or L. |
Conditions for Setting the DTC
The AT ISS calculated vehicle speed is 20 km/h (12 mph) or greater while the AT OSS calculated vehicle speed is 2 km/h (1 mph) or less for 10 seconds or greater.
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL). |
| • | The PCM limits the commanded gears to 2nd and 3rd gears. |
| • | The PCM records the operating conditions when the Conditions for Setting the DTC are met. The PCM stores this information as Freeze Frame and Failure Records. |
| • | The PCM stores DTC P0502 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 can clear the MIL/DTC. |
| • | The PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without an emission related diagnostic fault occurring. |
| • | The PCM cancels the DTC default actions when the ignition switch is OFF long enough in order to power down the PCM. |
Diagnostic Aids
| • | Inspect the connectors at the PCM, the AT OSS, and all other circuit connecting points for an intermittent condition. Refer to Testing for Intermittent Conditions and Poor Connections . |
| • | Inspect the circuit wiring for an intermittent condition. Refer to Testing for Electrical Intermittents . |
| • | Inspect for a disconnected AT OSS connector. |
| • | Inspect for an open or shorted AT OSS wire. |
| • | Inspect for a faulty AT OSS. |
| • | Inspect for an internal fault of the PCM. |
Step | Action | Values | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |||||||||
2 |
Important: Before clearing the DTCs, use the scan tool in order to record the Freeze Frame and Failure Records for reference. The Clear Info function will erase the data. 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. Does the scan tool indicate Transmission OSS parameter increasing when wheel speed increases? | -- | Go to Step 3 | |||||||||
3 |
Does the voltage measure near the specified value? | 5 V | Go to Step 4 | Go to Step 7 | ||||||||
4 | Measure the voltage from the OSS 5 volt reference circuit to the OSS low reference circuit. Does the voltage measure near the specified value? | 5 V | Go to Step 5 | Go to Step 8 | ||||||||
5 | Measure the voltage from the OSS high signal circuit to the OSS low reference circuit. Does the voltage measure near the specified value? | 5 V | Go to Step 9 | Go to Step 6 | ||||||||
6 | Test the OSS high signal circuit for the following conditions:
Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 11 | ||||||||
7 |
Important: The condition that affects this circuit may exist in other connecting branches of the circuit. Refer to Power Distribution Schematics for complete circuit distribution. Test the OSS 5 volt reference circuit for the following conditions:
Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 11 | ||||||||
8 | Test the OSS low reference circuit for an open or short to voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 11 | ||||||||
9 |
Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 10 | ||||||||
10 | Replace the OSS. Refer to Output Speed Sensor Replacement . Did you complete the repair? | -- | Go to Step 12 | -- | ||||||||
11 | Replace the PCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the repair? | -- | Go to Step 12 | -- | ||||||||
12 | In order to verify your repair, perform the following procedure:
Has the test run and passed? | -- | Go to Step 13 | Go to Step 2 | ||||||||
13 | With the scan tool, observe the stored information, capture info and DTC info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK |
