Circuit Description
The automatic transmission output speed sensor (OSS) provides vehicle speed information to the powertrain control module (PCM). The OSS is a permanent magnet generator mounted to the transmission case. The OSS produces an AC voltage as the transmission speed sensor rotor teeth pass through the sensor's magnetic field. The AC voltage level increases as the speed of the vehicle increases. The PCM converts the AC voltage into a digital signal. The PCM uses the vehicle speed signal to determine shift timing, torque converter clutch (TCC) apply, TCC release, and gear ratio calculations.
When the PCM detects a low output speed and the vehicle has a large engine speed in a drive gear, then DTC P0502 sets. DTC P0502 is a type B 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 MAP DTCs P0106, P0107 or P0108. |
| • | No TP DTCs P0122 or P0123. |
| • | No ISS DTCs P0716 or P0717. |
| • | The transmission is not in PARK or NEUTRAL. |
| • | The throttle position (TP) angle is greater than 12 percent. |
| • | The input speed is greater than 1,500 RPM. |
| • | The engine torque is greater than 68 N·m (50 lb ft). |
Conditions for Setting the DTC
The output speed is less than 150 RPM for 3 seconds.
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met. |
| • | The PCM commands maximum line pressure. |
| • | The PCM freezes transmission adaptive functions. |
| • | The PCM calculates output speed from input speed, engine speed, and commanded gear. |
| • | 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 during the second consecutive trip in which the Conditions for Setting the DTC are met. |
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. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step tests the ability of the OSS to produce an AC voltage. This step also verifies the integrity of the wiring to the PCM.
-
This step tests the OSS circuit for correct resistance.
Step | Action | Value(s) | Yes | No | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |||||||||||
2 |
Important: Before clearing the DTC, 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 Transmission OSS increase when the wheel speed increases? | -- | Go to Testing for Intermittent Conditions and Poor Connections | Go to Step 3 | ||||||||||
Can a voltage greater than the specified value be obtained? | 0.5 V AC | Go to Step 14 | Go to Step 4 | |||||||||||
Is the circuit resistance within the specified range? | 1,530-1,870 ohms | Go to Step 8 | Go to Step 5 | |||||||||||
5 | Is the circuit resistance greater than the specified value? | 1,870 ohms | Go to Step 11 | Go to Step 6 | ||||||||||
6 |
Is the circuit resistance less than the specified value? | 1,530 ohms | Go to Step 7 | Go to Step 13 | ||||||||||
7 | Test the high signal circuit and the low signal circuit of the OSS for being shorted together. Refer to Circuit Testing and Wiring Repairs. Did you find and correct the condition? | -- | Go to Step 15 | -- | ||||||||||
8 | Test the high signal circuit of the OSS for a short to ground. Refer to Testing for Short to Ground and Wiring Repairs. Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 9 | ||||||||||
9 |
Does the DMM display system voltage? | -- | Go to Step 10 | Go to Step 12 | ||||||||||
10 | Test the high signal circuit of the OSS for a short to voltage. Refer to Testing for a Short to Voltage and Wiring Repairs. Did you find and correct the condition? | -- | Go to Step 15 | -- | ||||||||||
11 |
Refer to Testing for Continuity and Wiring Repairs. Did you find and correct a condition? | -- | Go to Step 15 | Go to Step 13 | ||||||||||
12 |
Refer to Vehicle Speed Sensor Replacement .
Refer to Final Drive Assembly Disassemble or Output Speed Sensor Installation in Transmission Unit Repair Manual. Did you complete the repair? | -- | Go to Step 15 | -- | ||||||||||
13 | Replace the OSS. Refer to Vehicle Speed Sensor Replacement . Did you complete the replacement? | -- | Go to Step 15 | -- | ||||||||||
14 | Replace the PCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 15 | -- | ||||||||||
15 | Perform the following procedure in order to verify the repair:
Has the test run and passed? | -- | Go to Step 16 | Go to Step 2 | ||||||||||
16 | 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 |
