Refer to Engine Controls Schematics
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 more than 32 km/h (20 mph).
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 more than the transmission calculated speed by 32 km/h (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
| • | 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 Diagnostic Trouble Code (DTC) List/Type in Automatic Transmission 4L80-E if DTC P0722 or DTC P0723 is also set.
Test Description
Numbers below refer to step numbers on the diagnostic table:
-
Tests for B+ at VSS buffer.
-
Tests for proper ground path for VSS signal buffer.
-
Ensures that the replacement PCM, which utilizes an electrically erasable programmable read only memory (EEPROM), is programmed when installed.
Step | Action | Values | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
1 |
Important: Before clearing the DTCs, use the scan tool Capture Info to save the Freeze Frame and Failure Records for reference. The data in the control module is deleted once the Clear Info function is used. Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||||
2 |
With the drive wheels rotating, does the vehicle speed reading on the scan tool increase as the drive wheel speed increases? | -- | ||||||||
Is test lamp ON? | -- | |||||||||
Backprobe the VSS buffer module ignition feed circuit to the ground circuit with a unpowered test lamp. Is the test lamp ON? | -- | |||||||||
5 |
Does the voltage increase on the 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 tables 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 in Wiring Systems. Is the action complete? | -- | -- | |||||||
9 | Repair the open in the ground circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||
10 | Check the complete VSS input circuit for an open or short to ground. Refer to Wiring Repairs in Wiring Systems. Did you perform a repair? | -- | ||||||||
11 |
Did you perform a repair? | -- | ||||||||
12 |
Is there voltage present? | -- | ||||||||
13 |
Did you perform a repair? | -- | ||||||||
14 |
Did you perform a repair? | -- | ||||||||
15 | Replace the vehicle speed sensor (VSS). Refer to Vehicle Speed Sensor Replacement . Is the action complete? | -- | -- | |||||||
16 | Replace VSS buffer module. Refer to Vehicle Speed Sensor Buffer Replacement in Body and Accessories. Is the action complete? | -- | -- | |||||||
|
Important: The new PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . 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 |
