For 1990-2009 cars
Automatic Transmission Controls Schematics
Automatic Transmission Components

### Circuit Description

The Vehicle Speed Sensor (VSS) is a Permanent Magnet (PM) generator attached to the transmission case extension. 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 this AC voltage into a digital signal. The PCM uses the vehicle speed to determine the shift timing, the TCC apply and release, and the gear ratio calculations. The VSS voltage varies from 0.5 volts AC at 100 RPM to more than 100 volts AC at 6000 RPM. The VSS resistance value is 981-1864 ohms.

When the PCM detects a low vehicle speed with a high engine speed while in drive range, then DTC P0503 sets. DTC P0503 is a type A DTC.

### Conditions for Setting the DTC

• | The engine speed is more than 500 RPM for 5 seconds.

• | The engine is not in fuel shut off.

• | More than 6 seconds has elapsed since the last gear change.

• | The output speed does not rise more than 1000 RPM within 2 seconds.

• | The transmission is not in Park or Neutral.

• | The output speed drops more than 1500 RPM within 2 seconds.

### Action Taken When the DTC Sets

• | The transmission defaults to 3rd gear.

• | The PCM inhibits TCC operation.

• | The PCM illuminates the Malfunction Indicator Lamp (MIL).

### Conditions for Clearing the MIL/DTC

• | The PCM turns OFF the MIL after three consecutive ignition cycles 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

• | Check for Electromagnetic Interference (EMI) in circuits 400 and 401. EMI may be induced if the harness is routed along the spark plug wires.

• | Inspect the wiring for poor electrical connections at the PCM and at the VSS. Look for the following problems:

- | 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.

• | Ensure that the VSS is securely tightened to the case extension.

### Test Description

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

1. This step verifies that the PCM is receiving a signal from the vehicle speed sensor.

2. This step verifies that no opens exist in the circuitry from the vehicle speed sensor to the PCM connector.

3. This step performs a resistance test on the VSS circuits from the PCM connector.

#### DTC P0503 Vehicle Speed Sensor (VSS) Circuit -- Intermittent

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Were you sent here from the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check , Section 6
2 |

1. Install the Scan Tool .
2. 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.

3. Record the DTC Freeze Frame and Failure Records.
4. 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.

5. Start and idle the engine.
6. Place the transmission in drive range.
7. Select Output Speed on the scan tool.

With drive wheels rotating, does Transmission Output Speed increase when wheel speed increases?

--

Go to Diagnostic Aids

Go to Step 3

3 |

1. Turn the ignition switch to the OFF position.
2. Disconnect PCM connector C1.
3. Connect a J 39200 Digital Multimeter (DMM) to terminals 6 and 47 of the PCM connector C1.
4. Select AC volts on the DMM.
5. Rotate the Right drive wheel and observe the DMM.

Is the measured voltage greater than the specified value?

0.5 V

Go to Step 13

Go to Step 4

4 | Select ohms on the DMM. Is the resistance between terminals 6 and 47 greater than the specified value? | 1864 ohms | Go to Step 5 | Go to Step 6
5 | Inspect circuits 400 and 401 for an open. Repair the circuits if necessary. Refer to Troubleshooting Procedures, Section 8. Was a condition found and corrected? | -- | Go to Step 14 | Go to Step 10
6 | Does the DMM display a value less than the resistance specified? | 981 ohms | Go to Step 7 | Go to Step 8
7 | Inspect circuits 400 and 401 for a short together. Repair the circuits if necessary. Refer to Troubleshooting Procedures, Section 8. Was a condition found and corrected? | -- | Go to Step 14 | Go to Step 10
8 |

1. Connect one lead of the DMM to a good ground.
2. Connect the other lead to terminal 6, then terminal 47.

Is either resistance lower than the specified value?

50 K ohms

Go to Step 9

Go to Step 11

9 | Inspect circuits 400 and 401 for a short to ground. Repair the circuits if necessary. Refer to Troubleshooting Procedures, Section 8. Was a condition found and corrected? | -- | Go to Step 14 | Go to Step 10
10 | Remove the VSS and connect a DMM from terminal A to terminal B of the VSS. Is the measured resistance within the specified range? | 981-1864 ohms | Go to Step 11 | Go to Step 12
11 | Remove the VSS and inspect the Sensor Ring on the Final Drive Carrier Assembly for damage or misalignment. Was a condition found? | -- | Go to Unit Repair | Go to Diagnostic Aids
12 | Replace the Vehicle Speed Sensor. Refer to VSS Replacement, Section 7. Is the replacement complete? | -- | Go to Step 14 | --
13 | Replace the PCM. Refer to Powertrain Control Module Replacement/Programming , Section 6. Is the replacement complete? | -- | Go to Step 14 | --
14 | In order to verify your repair, perform the following procedure:

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

• | The engine speed is greater than 500 RPM for 5 seconds.

• | Not in fuel shut off.

• | The time since the last gear range change is greater than 6 seconds.

• | The output speed drop is less than 500 RPM for 5 seconds.

• | The output speed is greater than 1000 RPM for 2 seconds.

4. Select Specific DTC. Enter DTC P0503.

Has the test run and passed?

--

System OK

Begin the diagnosis again. Go to Step 1