DTC P0502 Vehicle Speed Sensor (VSS) Circuit Low Input 5.7L

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 rotor teeth on the transmission output shaft pass through the sensor's magnetic field. The AC voltage level and the number of pulses increase as the speed of the vehicle increases. The PCM converts the pulsing voltage to vehicle speed. The PCM uses the vehicle speed signal to determine shift timing and torque converter clutch (TCC) scheduling.

If the PCM detects a low vehicle speed when there is a high engine speed in a drive gear range, then DTC P0502 sets. DTC P0502 is a type B DTC.

Conditions for Running the DTC

• No MAF sensor DTCs P0101, P0102 or P0103.
• No MAP sensor DTCs P0107 or P0108.
• No TP sensor DTCs P0122 or P0123.
• No TFP manual valve position switch DTC P1810.
• The engine vacuum is 0-105 kPa.
• The engine torque is 30-400 lb ft.
• The TP angle is greater than 15%.
• The engine speed is greater than 3000 RPM.
• The transmission is not in PARK or NEUTRAL.

Conditions for Setting the DTC

The transmission output speed is less than 150 RPM for 2.5 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 second gear only.
• The PCM commands maximum line pressure.
• The PCM inhibits TCC engagement.
• The PCM freezes shift adapts from being updated.
• 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 fault no longer exists and/or the ignition switch is OFF long enough in order to power down the PCM.

Diagnostic Aids

• Inspect the connectors at the PCM, the VSS assembly and all other circuit connecting points for an intermittent condition. Refer to Testing for Intermittent and Poor Connections in Wiring Systems.
• Inspect the circuit wiring for an intermittent condition. Refer to Testing for Electrical Intermittents in Wiring Systems.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

2. Disable the traction control system when performing this step. When the ignition key is cycled to the OFF position and then cycled back ON, the traction control system defaults to ON.

3. This step tests the VSS assembly circuit.

4. This step tests the integrity of the VSS assembly.

DTC P0502 Vehicle Speed Sensor Circuit Low Input (5.7L) Step	Action	Value(s)	Yes	No
1	Did you perform the Powertrain Diagnostic System Check?	--	Go to Step 2	Go to A Powertrain On Board Diagnostic (OBD) System Check in Engine Controls
2	Install a Scan Tool . Turn ON the ignition, with the engine OFF. 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. Record the DTC Freeze Frame and Failure Records. Clear the DTC. Raise and support the rear axle assembly. Start the engine. Disable the traction control system. Place the transmission in any drive range. With the drive wheels rotating, does the Scan Tool Transmission OSS increase with the drive wheel speed?	--	Go to Diagnostic Aids	Go to Step 3
3	Turn OFF the ignition. Disconnect the PCM connector C2. Using the J 39200 digital multimeter (DMM) and the J 35616-A connector test adapter kit, measure the resistance between harness connector terminals C2-20 and C2-21. Does the resistance measure within the specified range?	1377-3355 ohms	Go to Step 4	Go to Step 7
4	Place the transmission in NEUTRAL. Select AC volts. Prevent one rear wheel from turning. Rotate the other rear wheel by hand, ensuring that the driveshaft is turning. Does the voltage measure greater than the specified value?	0.5 volts	Go to Step 5	Go to Step 12
5	Measure the resistance from terminal C2-21 to ground. Does the resistance measure greater than the specified value?	50 K ohms	Go to Step 6	Go to Step 9
6	Reconnect the PCM connector C2. Disconnect the engine wiring harness from the VSS assembly. Turn ON the ignition, with the engine OFF. Test the input circuit (CKT 821) of the VSS assembly for a short to power. Test the ground circuit (CKT 822) of the VSS assembly for a short to power. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition?	--	Go to Step 15	Go to Step 14
7	Disconnect the engine wiring harness from the VSS assembly. Measure the resistance of the VSS assembly. Does the resistance measure within the specified range?	1377-3355 ohms	Go to Step 8	Go to Step 13
8	Was the resistance measured in Step 3 greater than the specified value?	3355 ohms	Go to Step 10	Go to Step 11
9	Test the input circuit (CKT 821) of the VSS assembly for a short to ground. Test the ground circuit (CKT 822) of the VSS assembly for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition?	--	Go to Step 15	--
10	Test the input circuit (CKT 821) of the VSS assembly for an open. Test the signal circuit (CKT 822) of the VSS assembly for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition?	--	Go to Step 15	--
11	Test the input circuit (CKT 821) and the ground circuit (CKT 822) of the VSS assembly for a short together. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition?	--	Go to Step 15	--
12	Remove the VSS assembly. Inspect the output shaft speed sensor rotor for damage or misalignment. Inspect the case extension bushing for wear. Did you find and correct the condition?	--	Go to Step 15	Go to Step 13
13	Replace the VSS assembly. Refer to Vehicle Speed Sensor Replacement . Did you complete the replacement?	--	Go to Step 15	--
14	Replace the PCM. Refer to PCM Replacement/Programming in Engine Controls. Did you complete the replacement?	--	Go to Step 15	--
15	Perform the following procedure in order to verify the repair: Select DTC. Select Clear Info. Operate the vehicle, so that the transmission output speed is greater than 250 RPM for 2 seconds. Select Specific DTC. Enter DTC P0502. Has the test run and passed?	--	System OK	Go to Step 1