DTC P0502 Vehicle Speed Sensor (VSS) Circuit Low Input. Chevrolet Tahoe

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 1996 🢒 Tahoe - 2WD 🢒 Transmission/Transaxle 🢒 Automatic Transmission - 4L80-E 🢒 DTC P0502 Vehicle Speed Sensor (VSS) Circuit Low Input

DTC P0502 Vehicle Speed Sensor (VSS) Circuit Low Input 5.7L and 7.4L Gas

Automatic Transmission Components 5.7L and 7.4L Gas
Automatic Transmission Controls Schematics 5.7L and 7.4L
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The OSS Sensor, which is a Permanent Magnet (PM) generator, gives the vehicle speed information to the VCM. The PM generator produces a pulsing AC voltage. The AC voltage level and the number of pulses increase as the speed of the vehicle increases. The VCM then converts the pulsing voltage to vehicle speed. The vehicle speed is used for calculations. A scan tool can display the vehicle speed.

When the VCM detects a low vehicle speed and there is a high engine speed in a drive gear range, DTC P0502 sets. DTC P0502 is a type "D" DTC. For California emissions, DTC P0502 is a type "A" DTC.

Conditions for Setting the DTC

•	No TP Sensor DTCs P0122 or P0123.

•	No TFP Val. Position Sw. P1810

•	No ISS Sensor low DTC P0717.

•	The engine torque must be 80 lb ft (60 N·m) to the following:

-	275 lb ft (345 N·m)

-	375 lb ft (470 N·m) (5.7L)

-	500 lb ft (627 N·m) (7.4L)

•	The Input speed is greater than 2500 RPM.

•	The transmission is not in Park or Neutral.

•	The engine is running and not in fuel cut off.

•	The output shaft speed is less than 200 RPM for at least 3 seconds.

Action Taken When the DTC Sets

•	The VCM commands maximum line pressure.

•	The VCM freezes the shift adapts.

•	The VCM defaults a calculated output speed value by using the Input Speed Sensor values.

•	For California emissions, the VCM illuminates the Malfunction Indicator Lamp (MIL).

Conditions for Clearing the MIL/DTC

•	For California emissions, the VCM turns off the MIL after three consecutive ignition cycles without a failure reported.

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

•	The VCM cancels the DTC default actions when the fault no longer exists and the ignition is cycled "off" long enough to power down the VCM.

Diagnostic Aids

•	DTC P0502 sets when no vehicle speed is detected at the start off.

•	Inspect the wiring for poor electrical connections at the VCM. Inspect the wiring for poor electrical connections at the transmission 20-way connector. Look 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.

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

•	First diagnose and clear any engine DTCs or TP Sensor codes. Then inspect for any transmission DTCs that may have reset.

Test Description

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

This step tests the VSS circuit.

This step tests the integrity of the VSS.

This step tests the 5-volt and ground circuit of the VCM.

DTC P0502 Vehicle Speed Sensor Low Input (Transmission Output Shaft Speed Signal)

Step	Action	Value(s)	Yes	No
1	Was the Powertrain On-Board Diagnostic (OBD) System Check performed?	--	Go to Step 2	Go to Powertrain On Board Diagnostic (OBD) System Check
2	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 and Failure Records for reference. The Clear info function will erase the data. Record the DTC Freeze Frame and Failure Records. Raise the drive wheels. Start the engine. Place the Transmission in any drive range. With the drive wheels rotating, does the Trans OSS increase with the drive wheel speed?	--	Go to Diagnostic Aids	Go to Step 3
3	Does the speedometer work?	--	Go to Step 4	Go to Step 6
4	Inspect for the most current calibration. Inspect for an incorrect calibration. Refer to the Service Bulletin. Is the calibration current?	--	Go to Step 15	Go to Step 5
5	Reprogram the VCM. Refer to EEPROM Programming . Have you reprogrammed the VCM?	--	Go to Step 16	--
6	Turn the ignition off. Disconnect the C1 (blue) VCM connector. Using the J 39200 DVOM and the J 35616-A Connector Test Adapter Kit, measure the resistance between the VCM connector terminals C1-29 and C1-30.	1480-2700ohms	Go to Step 7	Go to Step 8
7	Place the transmission in Neutral. Select the AC volts. Rotate the rear wheels, ensuring that the driveshaft is turning. Is the voltage greater than the specified value?	0.5 Volts	Go to Step 9	Go to Step 10
8	Inspect circuits 821 and 822 for a poor connection or an open circuit. Did you find a poor connection or an open circuit?	--	Go to Step 16	Go to Step 10
9	Reconnect the C1 (blue) VCM connector. Disconnect the OSS Sensor harness from the OSS Sensor. With the engine off, turn the ignition switch to the RUN position. Using the J 39200 DVOM, measure the voltage at the OSS Sensor harness connector terminals A and B. Is the J 39200 DVOM showing 4.0-5.1 volts?	4.0-5.1 volts	Go to Step 15	Go to Step 12
10	Remove the OSS Sensor. Inspect the output shaft speed sensor rotor for damage or misalignment. Did you find a problem ?	--	Go to Step 16	Go to Step 11
11	Replace the OSS Sensor. Refer to Automatic Transmission Output Shaft Speed Sensor Replacement, in On-Vehicle Service. Is the replacement complete?	--	Go to Step 16	--
12	Was the reading in Step 9 less than the specified value?	4.0 volts	Go to Step 15	Go to Step 13
13	Was the reading in Step 9 greater than the specified value?	5.1 volts	Go to Step 14	--
14	Repair the short to power B+ in circuit 821. Refer to Electrical Diagnosis, Section 8. Is the repair complete?	--	Go to Step 16	--
15	Replace the VCM. Refer to VCM Replacement/Programming , Section 6. Is the replacement complete?	--	Go to Step 16	--
16	In order to verify your repair, perform the following procedure: Select DTC. Operate the vehicle so that the transmission output speed is grater than 500 RPM for 1 second. Select Clear Info. Select Specific DTC. Enter DTC P0502. Has the test run and passed?	--	System OK	Begin the diagnosis again. Go to Step 1

DTC P0502 Vehicle Speed Sensor (VSS) Circuit Low Input 6.5L Diesel

Automatic Transmission Components 6.5L Diesel
Automatic Transmission Controls Schematics 6.5L
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

Circuit Description

Circuit 439 is the ignition voltage feed for the PCM. Circuit 440 is the battery feed for the PCM.

When the PCM detects a low voltage, a high voltage for a long time, or a high voltage for a short time, then DTC P0560 sets. DTC P0560 is a type D DTC.

Conditions for Setting the DTC

System Voltage Low:

•	The engine speed is greater than 1500 RPM.

•	The system voltage is less than 10.5 volts at a maximum transmission temperature of 152°C (305°F).

•	The system voltage is less than 6.7 volts at a minimum transmission temperature of -40°C (-40°F).

•	All conditions met for 4 seconds.

If the system voltage is high then the system voltage is greater than 19 volts for 4 seconds.

Action Taken When the DTC Sets

•	The PCM causes an immediate landing to second gear.

•	The PCM turns off the PC Sol. Valve.

•	The PCM inhibits the TCC engagement.

•	The PCM freezes the shift adapts.

•	The PCM does NOT illuminate the Malfunction Indicator Lamp (MIL).

Conditions for Clearing the DTC

•	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.

•	The PCM cancels the DTC default actions when the ignition is cycled OFF long enough to power down the PCM.

Diagnostic Aids

•	Charging the battery with a battery charger and jumpstarting an engine may set DTCs.

•	If this DTC is set when an accessory is operated, inspect for faulty connections or an excessive current draw.

•	Inspect for faulty electrical connections at the starter solenoid.

•	Inspect for faulty electrical connections at the fusible link.

•	Inspect for loose or damaged terminals at the generator.

•	Inspect the generator belt wear and the generator belt tension.

•	First diagnose and clear any engine DTCs or APP Sensor codes that are present. Then inspect for any transmission DTCs that may have reset.

Test Description

This step tests the charging system voltage.

This step tests the battery voltage input at the PCM.

This step tests the ignition voltage inputs at the PCM.

P0560

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

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 and Failure Records for reference. The Clear Info function will erase the data.

Record the DTC Freeze Frame and Failure Records.
If any DTCs are present, refer to their applicable diagnostic tables before continuing.
Using the J 39200 DVOM, measure the battery voltage across the battery terminals.
Record the battery voltage measurement for future reference.

Is the voltage higher than the specified value?

10.5 volts

Go to Step 3

Go to Engine Electrical, Section 6

Start the engine.
Allow the engine to warm to normal operating temperature.

Is the generator lamp ON?

Go to Engine Electrical, Section 6

Go to Step 4

Increase the engine speed to greater than 1500 RPM.
Observe the scan tool system voltage.

Is the system voltage within the specified range?

13-15 volts

Go to Step 5

Go to Engine Electrical, Section 6

Turn the ignition switch OFF.
Disconnect the C3-C13 (blue) PCM connector (Additional DTCs will set).
With the engine OFF, turn the ignition switch ON.
Measure the battery voltage input at the PCM connector terminal C13-C13. Use the J 39200 DVOM and the J 35616-A Connector Test Adaptor Kit.

Is there a voltage variance between the voltage measured at the battery (taken in Step 2) and at terminal C3-C13 that is greater than the specified value?

0.5

Go to Step 6

Go to Step 7

Repair the high resistance condition in circuit 440.

Refer to Electrical Diagnosis, Section 8.

Did you repair the circuit?

Go to Step 11

Disconnect the C3 PCM connector.
Measure the ignition voltage input at the PCM connector terminals C3-C11.

Is there a voltage variance between the voltage measured at the battery (taken in Step 2) and at terminals C3-C11 that is greater than the specified value?

0.5 volts

Go to Step 8

Go to Step 9

Repair the high resistance condition in circuit 439.

Refer to Electrical Diagnosis, Section 8.

Did you repair the circuit?

Go to Step 11

Inspect the PCM connector terminals J3-C13 and C3-C11 for damaged, or backed out connector pins.
Inspect for weak terminal tension.

Did you find a problem?

Go to Step 11

Go to Step 10

Replace the PCM.

Refer to Powertrain Control Module Replacement/Programming Section 6.

Is the replacement complete?

Go to Step 11

In order to verify your repair, perform the following procedure:

Select DTC.
Select Clear Info.
Operate the vehicle under the following conditions:

•	Start the vehicle.

•	Warm the vehicle to normal operating temperature.

•	Inspect that the PCM sees a system voltage between 8.3 and 18.9 volts.

Select Specific DTC. Enter DTC P0560.

Has the test run and passed?

System OK

Begin diagnosis again. Go to Step 1