DTC P0502 Vehicle Speed Sensor (VSS) Circuit Low Input. Cadillac Eldorado 1998

For 1990-2009 cars only

Makes 🢒 Cadillac 🢒 1998 🢒 Eldorado 🢒 DTC 🢒 DTC P0502 Vehicle Speed Sensor (VSS) Circuit Low Input

Automatic Transmission Components
Automatic Transmission Controls Schematics
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 Powertrain Control Module (PCM). The PCM converts the AC voltage into a digital signal. The PCM uses the vehicle speed in order to determine shift timing, Torque Converter Clutch (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.

If 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 B DTC.

Conditions for Setting the DTC

•	No MAF DTCs P0101, P0102 or P0103.

•	No TP DTCs P0121, P0122 or P0123.

•	No A/T ISS DTCs P0716 or P0717.

•	No TFP Val. Position Sw. DTC P1810.

•	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 degrees.

•	The input shaft speed is 2000 RPM or greater.

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

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 inhibits TCC engagement.

•	The PCM disables the cruise control.

•	The PCM disables steady state adapts.

•	The PCM disables upshift adapts.

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

•	DTC P0502 is stored in the PCM history.

Conditions for Clearing the MIL/DTC

•	The PCM turns OFF the MIL after three consecutive trips 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 at the PCM, and the VSS 2-way connector for the following conditions:

-	A bent terminal

-	A backed out terminal

-	A damaged terminal

-	Poor terminal tension

-	A chafed wire

-	A broken wire inside the insulation

-	Moisture intrusion

•	When diagnosing for an intermittent short or open, 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 checks for DTCs and for a vehicle speed signal. It is important to record Freeze Frame and Failure Record information before proceeding further.

This step has the Scan Tool verify that the correct calibration is in the PCM.

This step tests for a resistance value greater than 1950 ohms which would indicate a possible open in circuit 400 or circuit 401.

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 circuit 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 circuit 400 or circuit 401.

DTC P0502 Vehicle Speed Sensor Circuit Low Input

Step

Action

Value(s)

Yes

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

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check in Engine Controls

Install the Scan Tool .
With the engine OFF, turn the ignition switch to the RUN position.

Important: Before clearing the DTC(s), use the Scan Tool in order to record the Freeze Frame and Failure Records for reference. Using the Clear Info function will erase the stored Freeze Frame and Failure Records from the PCM.

Record the DTC Freeze Frame and Failure Records, then clear the DTC(s).
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.

Start the engine and idle the engine.
Place the transmission in drive range.
Select Transmission OSS RPM on the Scan Tool .

With the drive wheels rotating, does the Transmission OSS RPM increase when the wheel speed increases?

Go to Diagnostic Aids

Go to Step 3

Turn the ignition OFF.
Disconnect PCM connector C2.
Using the J 35616 Connector Test Adapter Kit, Connect the J 39200 DMM from terminal 7 to terminal 8 of the PCM connector.
Select AC volts on the J 39200 DMM.

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