Refer to Engine Controls Schematics
Cell 22: VSS Controls
.
Circuit Description
The speed sensor circuit consists of a magnetic induction type sensor, a vehicle speed sensor buffer module and wiring. The magnetic reluctor pressed on the output shaft induces an alternating current in the sensor. The A/C voltage signal is transmitted to the buffer. The buffer compensates for various axle ratios tire sizes and converts the signal into a square wave for use by the speedometer, the cruise control, the antilock brake, and the PCM. The buffer sends the following two different signals to the PCM:
| • | A VSS signal |
| • | An output shaft speed signal for the automatic transmission |
Conditions for Running the DTC
| • | The vehicle speed is greater than 20 mph. |
| • | The four wheel low is not selected. |
Conditions for Setting the DTC
The VSS buffer calculated speed is less than half of the transmission calculated speed.
or
| • | The VSS buffer calculated speed is greater than the transmission calculated speed by 20 mph. |
| • | All of the conditions must be met for 2 seconds. |
Action Taken When the DTC Sets
| • | The PCM will not illuminate the malfunction indicator lamp (MIL). |
| • | The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn the MIL off after 3 consecutive trips without a fault condition. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures. |
| • | The scan tool Clear Info function was used. |
Diagnostic Aids
Check the connections at the VSS buffer and the PCM. Refer to 4L80-E Diagnostic Trouble Codes if DTC P0722 or DTC P0723 is also set.
Test Description
Number(s) below refer to number(s) on the Diagnostic Table.
-
This tests for B+ at VSS buffer.
-
This tests for proper ground path for vehicle speed sensor signal buffer.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 |
Important: Before clearing the DTCs, use the scan tool Capture Info function to save the Freeze Frame and the Failure records for reference. The control module's data is deleted once the Clear Info function is used. Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||
2 |
With the drive wheels rotating, does the vehicle speed increase as the drive wheel speed increases? | -- | ||
Is test lamp ON? | -- | |||
Back probe the VSS buffer module ignition feed circuit to the ground circuit with a J 35616-200 unpowered test lamp. Is the test lamp ON? | -- | |||
5 |
Does the voltage increase on the J 39200 DMM as the drive wheel speed increases? | -- | ||
6 | Does the scan tool display a transmission output speed (MPH) increase as the drive wheel speed increases? | -- | ||
7 | DTC is intermittent. If no additional DTCs are stored, refer to Diagnostic Aids. If additional DTCs are stored refer to those table(s) first. Are any additional DTCs stored? | -- | Go to the applicable DTC Table | Go to Diagnostic Aids |
8 | Repair the open in the ignition feed circuit. Refer to Wiring Repairs . Is the action complete? | -- | -- | |
9 | Repair the open in the ground circuit. Refer to Wiring Repairs . Is the action complete? | -- | -- | |
10 | Check the complete VSS input circuit for an open or short to ground. Refer to Wiring Repairs . Did you perform a repair? | -- | ||
11 |
Did you perform a repair? | -- | ||
12 |
Is there voltage present? | -- | ||
13 | Check the VSS output circuit for an open or short to ground. Repair the VSS output circuit as necessary. Refer to Wiring Repairs . Did you perform a repair? | -- | ||
14 | Check VSS output circuit for poor connections at the PCM. Repair as necessary. Refer to Wiring Repairs . Did you perform a repair? | -- | ||
15 | Replace the Vehicle Speed Sensor. Refer to Vehicle Speed Sensor Replacement 4L60 E or Vehicle Speed Sensor Replacement 4L80 E in Automatic Transmission. . Is the action complete? | -- | -- | |
16 | Replace VSS Buffer module. Refer to Vehicle Speed Sensor Buffer Replacement in Body and Accessories. Is the action complete? | -- | -- | |
17 |
Important: The new PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Is the action complete? | -- | -- | |
18 |
Does the scan tool indicate the diagnostic Passed? | -- | ||
19 | Does the scan tool display any additional undiagnosed DTCs? | -- | Go to the applicable DTC Table | System OK |
