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For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2001 🢒 Chevy C Cab/Chassis HD (GMT 400) 🢒 Transmission/Transaxle 🢒 Manual Transmission - NV 4500 🢒 DTC P0501

DTC P0501 Diesel

Refer to the VSS Circuit part of Engine Controls Schematics in Engine Controls - 6.5L.

Circuit Description

The speed sensor circuit consists of a magnetic induction type sensor, a vehicle speed sensor buffer module and wiring. Gear teeth pressed on the output shaft induce an alternating current in the sensor. This signal is transmitted to the buffer. The buffer compensates for various axle ratios and converts the signal into a square wave for use by the speedometer, cruise control, antilock brake and powertrain control module (PCM). The buffer sends two different signals to the PCM.

Conditions for Setting the DTC
    • The PCM performs this DTC diagnostic continuously.
    • The vehicle speed is greater than 32 km/h (20 mph).
    • The four wheel low is not selected.
    • The VSS buffer calculated speed is less than half the transmission calculated speed.
    • All of the Conditions for Setting the DTC are met for 2 seconds.

or

    • The PCM performs this DTC diagnostic continuously.
    • The VSS buffer calculated speed is greater than transmission calculated speed by 32 km/h (20 mph).
    • All of the diagnostic set conditions met for 2 seconds.

Action Taken When the DTC Sets
    • The PCM disallows all cruise control inputs.
    •  The PCM will not illuminate the malfunction indicator lamp (MIL).
    • The PCM records the operating conditions at the time the diagnostic fails. This information stores in the Failure Records.

Conditions for Clearing the MIL/DTC
    • A History DTC will clear when 40 consecutive warm-up cycles, during which the diagnostic does not fail, coolant temperature has risen 5°C (40°F) from the start up coolant temperature, and the engine coolant temperature exceeds 71°C (160°F) during that same ignition cycle.
    • A scan tool can clear the MIL/DTC.

Test Description

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

  1. This tests for B+ at VSS buffer.

    2.

  2. This tests for proper ground path for vehicle speed sensor signal buffer.

Step

Action

Value(s)

Yes

No

1

Important: Before clearing any DTCs, use the scan tool Capture Info to save freeze frame and failure records for reference, as the scan tool loses data when using the Clear Info function.

Did you perform the Diagnostic System Check - Manual Transmission ?

--

Go to Step 2

Go to Diagnostic System Check - Manual Transmission

2
  1. Install a scan tool.
  2. Raise the drive wheels.
  3. Start the engine.
  4. Disable the traction control system, if equipped.
  5. Shift the transmission into third gear.
  6. Slowly release the clutch.

With the drive wheels rotating, does the vehicle speed increase with drive wheel speed increase?

--

Go to Intermittent Conditions in Engine Controls - 6.5L

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Shift the transmission into NEUTRAL.
  3. Back probe the VSS buffer module ignition feed circuit with a test light connected to ground.

Is the test light ON?

--

Go to Step 4

Go to Step 7

4

Back probe the VSS buffer module ignition feed circuit to the ground circuit with a test light.

Is the test light ON?

--

Go to Step 5

Go to Step 8

5
  1. Back probe the VSS buffer module at the VSS input circuit (C7) to the other VSS input circuit (C12) with a DMM on the AC scale.
  2. Place the transmission in any drive range with the drive wheels rotating.

Does the voltage increase on the DMM with drive wheel increase?

--

Go to Step 6

Go to Step 9

6

Does the scan tool display a trans output speed (mph) increase with drive wheel increase?

--

Go to Step 12

Go to Step 11

7

Repair the open in the ignition feed circuit.

Is the action complete?

--

Go to Step 17

--

8

Repair the open in the ground circuit.

Is the action complete?

--

Go to Step 17

--

9

Test the complete VSS input circuit for an open or short to ground.

Was a repair performed?

--

Go to Step 17

Go to Step 10

10
  1. Test the VSS connector for an open or high resistance condition.
  2. If a condition is found, repair the condition as necessary.

Was a condition found?

--

Go to Step 17

Go to Step 14

11
  1. Back probe the VSS buffer module at the VSS output circuit (C15) with a DMM connected to ground.
  2. Place the transmission in any drive range with the drive wheels rotating.

Is there voltage present?

--

Go to Step 12

Go to Step 15

12

Test the VSS output circuit for an open or short to ground.

Was a repair performed?

--

Go to Step 17

Go to Step 13

13

Test the VSS output circuit connections at the PCM for an open or high resistance condition.

Was a repair performed?

--

Go to Step 17

Go to Step 16

14

Replace the vehicle speed sensor. Refer to Vehicle Speed Sensor .

Is the action complete?

--

Go to Step 17

--

15

Replace the VSS Buffer module. Refer to Vehicle Speed Sensor Module Replacement in Instrument Panel, Gages, and Console.

Is the action complete?

--

Go to Step 17

--

16

Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls - 6.5L.

Is the action complete?

--

Go to Step 17

--

17
  1. Using the scan tool, clear the DTCs.
  2. Start the engine and idle at normal operating temperature.
  3. Select DTC, Specific, then enter the DTC number which was set.
  4. Operate the vehicle within the Conditions for Setting the DTC, until the scan tool indicates the diagnostic Ran.

Does the scan tool indicate the diagnostic Passed?

--

System OK

Go to Step 2