DTC P0502 Vehicle Speed Sensor (VSS) Circuit Low Input. Cadillac DeVille 1996

For 1990-2009 cars only

Makes 🢒 Cadillac 🢒 1996 🢒 DeVille 🢒 DTC 🢒 DTC P0502 Vehicle Speed Sensor (VSS) Circuit Low Input

Automatic Transmission Components
Brake Switch, Solenoids, and VSS
Handling ESD Sensitive Parts Notice
OBD II Symbol Description Notice

Circuit Description

The Vehicle Speed Sensor (VSS) is a Permanent Magnet (PM) generator attached to the transmission case. The final drive assembly has a toothed wheel (VSS rotor). As the final drive assembly rotates, an AC voltage is induced and transmitted to the PCM. The PCM converts the AC voltage into a digital signal. The PCM uses the vehicle speed in order to determine shift timing, TCC apply and release, and gear ratio. The VSS voltage will vary from 0.5 volts AC at 100 RPM to more than 100 volts AC at 8000 RPM. The VSS resistance value is 1300-1950 ohms.

When the PCM detects a low vehicle speed and a high Input Shaft Speed sensor signal while in a drive range, then DTC P0502 sets. DTC P0502 is a Type A DTC.

Conditions for Setting the DTC

•	No MAF P0101, P0102 or P0103 DTCs are set.

•	No TP sensor P0121, P0122 or P0123 DTCs are set.

•	No Automatic Transmission Input (Shaft) Speed sensor P0716 or P0717 DTCs are set.

•	No TFP Valve Position Switch P1810 DTC is set.

•	The transmission is not in Park, Neutral, or Reverse.

•	The delivered torque is greater than 109 N·m (80 lb ft).

•	The TP angle is greater than 12.8°.

•	The vehicle speed is 8 km/h (5 mph) or less for 2 seconds.

•	The input shaft speed is 2000 RPM or greater.

Action Taken When the DTC Sets

•	The PCM illuminates the Malfunction Indicator Lamp (MIL).

•	SERVICE ENGINE SOON, SPEED SENSOR FAULT displays on the Driver Information Center (DIC).

•	The PCM commands default line pressure.

•	The PCM disables steady state adapts.

•	The PCM disables upshift adapts.

•	The PCM inhibits the TCC.

•	The PCM inhibits torque management.

•	The PCM calculates vehicle speed from the Automatic Transmission Input (Shaft) Speed sensor and commanded gear.

•	The PCM disables the cruise control.

Conditions for Clearing the MIL/DTC

•	The PCM turns OFF the MIL after three consecutive ignition cycles without a failure reported.

•	A scan tool can clear the DTC from the PCM history. The PCM clears the DTC from the PCM history if the vehicle completes 40 warm-up cycles without a failure reported.

•	The PCM cancels the DTC default actions when the fault no longer exists and the ignition is OFF long enough in order to power down the PCM.

Diagnostic Aids

•	Inspect the wiring for poor electrical connections at the PCM. Inspect the wiring for poor electrical connections at the VSS 2-way connector. Inspect for the following conditions:

-	A bent terminal

-	A backed out terminal

-	A damaged terminal

-	Poor terminal tension

-	A chafed wire

•	When diagnosing for an intermittent short or open condition, massage the wiring harness while watching the test equipment for a change.

•	Check for Electromagnetic Interferences (EMI) induced on circuits 400 and 401 by a misrouted harness along spark plug wires.

Test Description

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

This Step ensures that the Powertrain On-Board Diagnostic System Check was performed.

This Step checks for DTCs and for a vehicle speed signal. It is important to record freeze frame or failure record information before proceeding further.

Important: Place the gear select lever in the Neutral position before rotating the wheel.

This Step tests for an AC voltage at the PCM.

This Step has the scan tool verify that the correct calibration is in the PCM.

This Step performs a resistance check on the VSS circuits from the PCM connector.

This Step verifies that the ohmmeter displays a resistance value greater than 1950 ohms. Circuits 400 and 401 must be checked for an open.

This Step verifies that the ohmmeter displays a value less than or equal to the specified VSS value. Resistance less than 1300 implies that the circuits are shorted together. Resistance within specification implies that circuit 400 or 401 is a possible short to ground.

This Step performs a resistance check on the VSS, if no opens, shorts to ground or shorts together were found on the 400 or 401 circuits.

This Step verifies that the ohmmeter displays a resistance value less than or greater than specified.

This Step replaces the PCM after testing the component and circuitry.

This Step road tests the vehicle to ensure that the repair is complete.

DTC P0502 Vehicle Speed Sensor Circuit (VSS) Low Input

Step

Action

Value(s)

Yes

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

Go to Step 2

Go to A Powertrain On Board Diagnostic (OBD) System Check

Install the scan tool (tech 1) .
With the engine OFF, turn the ignition switch to the RUN position.

Important: Before clearing the DTCs, use the scan tool in order to record the Freeze Frame or Failure Records for reference. The Clear Info function will erase the data.

Record the DTC Freeze Frame and Failure Records.
Raise and support the drive wheels.

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.