PT Cruiser, 2001 - 2005

Vehicle Speed Control


Description & Operation

Interactive Speed Control (used on A/T only) means that communication between the PCM and the TCM is taking place. Interactive speed control avoids unnecessary shifting for smoother, quieter operation and when downshifts are required, makes the shifts smoother.

When climbing a grade the interactive speed control tries to maintain the set speed by increasing the throttle opening, while inability/delaying downshifts.

If opening the throttle alone cannot maintain the set speed and the vehicle speed drops more than 3 mph below the set speed, the transmission will downshift to third gear. If the vehicle continues to lose speed, by more than 6 mph, the transmission will downshift again maintain the set speed. After the vehicle encounters a less-steep grade, or has crested the grade (reduced the load on the powertrain) and can maintain the set speed at a reduced throttle position, the transmission will upshift, as appropriate, until the set speed can be maintained in Overdrive.

Downshift delay features have been added to reduce the number and frequency of downshifts when operating in hilly or mountainous country.

While operating, interactive speed control delays or avoids downshifts by allowing up to nearly wide open throttle without the TCM scheduling a downshift. If the interactive speed control is not engaged or if the throttle is manually overridden by the driver while interactive speed control is engaged, the downshift delay feature is not activated.

Torque converter lock and unlock shifts are not affected by the downshift delay feature and will occur at the same throttle angle at a given speed regardless of whether interactive speed control operates or not.

All vehicles equipped with a four speed automatic transmission have a grade hunting feature for the 2nd to 3rd gear upshift and the 3rd to Overdrive upshift.

The TCM identifies the powertrain loading conditions and selects the proper gear to maintain the current vehicle speed. Under moderate loading conditions the transaxle will stay in 3rd gear until the top of the grade is reached or the powertrain loading is reduced.

If powertrain loading is severe, the transaxle may shift into 2nd gear and remain there until powertrain loading is reduced, then a 2nd to 3rd gear upshift will be scheduled. Grade hunting features always operate regardless of whether or not the interactive speed control is engaged.

If the interactive speed control is not engaged and powertrain loading is not reduced, the driver may have to completely lift off of the throttle before an upshift will occur.

If the driver does lift off the throttle to induce an upshift under these conditions, vehicle speed will reduce and the Overdrive to 3rd and 3rd to 2nd gear downshifts will reoccur when the throttle is reapplied. If grade-hunting is repeatedly induced by the driver, transaxle damage may result.

Transmission control software includes an automatic speed control overspeed reduction feature. This maintains vehicle speed at the selected set point when descending a grade.

The Transmission Control Module (TCM) first senses that the speed control is set. If the set speed is exceeded by more than 4 mph (6.5 km/hr) and the throttle is closed, the TCM causes the transaxle to downshift to THIRD gear. After downshifting, the automatic speed control resumes normal operation. To ensure that an upshift is appropriate after the set speed is reached, the TCM waits until the speed control system opens the throttle at least 6 degrees before upshifting to OVERDRIVE again.

If the driver applies the brakes, canceling automatic speed control operation with the transaxle still in THIRD gear, the TCM maintains this gear until the driver opens the throttle at least 6 degrees to avoid an inappropriate upshift. The upshift is also delayed for 2.5 seconds after reaching the 6 degrees throttle opening in anticipation that the driver might open the throttle enough to require THIRD gear. This will avoid unnecessary and disturbing transmission cycling. If the automatic speed control RESUME feature is used after braking, the upshift is delayed until the set speed is achieved to reduce cycling and provide better response.

The speed control system is electronically controlled and vacuum operated. The electronic control is integrated into the Powertrain Control Module, located on the left side of the engine compartment next to the air cleaner. The controls are located on the steering wheel and consist of a single switch. The ON, OFF, RESUME, ACCEL, SET, COAST, and CANCEL, lever is located on the right of the steering wheel. The system is designed to operate at speeds above 25 mph (40 km/h)


When speed control is activated by depressing the ON switch, the PCM allows a set speed to be stored in RAM for speed control. To store a set speed, depress the SET switch while the vehicle is moving at a speed between 25 and 85 mph. In order for the speed control to engage, the brakes cannot be applied, nor can the gear selector be indicating the transmission is in Park or Neutral.

The speed control can be disengaged manually by:

Stepping on the brake pedal
Depressing the OFF switch
Depressing the CANCEL switch.
Depressing the clutch pedal

Depressing the OFF switch or turning off the ignition switch will erase the set speed stored in the PCM.

For added safety, the speed control system is programmed to disengaged for any of the following conditions:

An indication of Park or Neutral
A rapid increase rpm (indicates that the clutch has been disengaged)
Excessive engine rpm (indicates that the transmission may be in a low gear)
The speed signal increases at a rate of 10 mph per second (indicates that the co-efficient of friction between the road surface and tires is extremely low)
The speed signal decreases at a rate of 10 mph per second (indicates that the vehicle may have decelerated at an extremely high rate)

Once the speed control has been disengaged, depressing the RESUME switch when speed is greater than 25 mph allows the vehicle to resume control to the target speed that was stored in the PCM.

While the speed control is engaged, the driver can increase the vehicle speed by depressing the ACCEL switch. The new target speed is stored in the PCM when the ACCEL switch is released. The PCM also has a tap-up feature in which target speed increases by 2 mph for each momentary switch activation of the ACCEL switch. The PCM also provides a means to decelerate to a new lower target speed without disengaging speed control. Depress and hold the COAST switch until the desired speed is reached, then release the switch.

Speed Control Switches

The switches are mounted on a stalk extending from the right side of the steering wheel hub. It rotates with the steering wheel. The switch cannot be repaired. If the switch fails, the entire switch module must be replaced.

The speed control system has five separate voltage inputs that are provided from a single multiplexed (MUX) switch that supplys different voltage inputs to the PCM. The switch names are: ON, OFF, SET, COAST, RESUME, ACCEL, and CANCEL. Based on conditions when the buttons or lever is pushed or pulled (and released), the five voltages ranges provided to the PCM result in the following functions: ON, OFF, SET, COAST, RESUME, ACCEL, and CANCEL.

All the functions are included, but they operation of the switch is different then most other applications. A push button in the end of the stalk toggles the system voltage between turning the speed control system on (for the first press) and off (for the second press) The word Cruise will then illuminate on the cluster. Pushing the stalk down sets the cruise to maintain the current vehicle speed and is set into memory. Holding the stalk down allows the vehicle to coast to a lower speed. Pushing the stalk up causes the vehicle to resume the previously set speed that is set in memory. Holding it in the up position causes the vehicle speed to increase until the switch is released or the maximum allowable set speed is reached. Pulling the stalk toward the steering wheel cancels the operation of the speed control, allowing the vehicle to coast, but retaining the set speed in memory. Moving the stalk up momentarily causes the set speed to in crease by 2 mph. Repeated movement of the stalk in the same direction has a cumulative effect on the set speed. The minimum set speed is reduced to 25 mph and a maximum set speed is 85 mph.

Vehicle Speed Signal Automatic Transaxles

On A/T vehicles, the transaxle control module (TCM) supplies the vehicle speed signal to the PCM based on the output shaft speed. The PCM sends a 5-volt signal to the TCM. The TCM switches this signal to a ground, and then opens the circuit at a rate of 8000 pulses per mile. When the PCM counts 8000 pulses, the PCM assumes the vehicle has traveled one mile. The output speed sensor is located on the side of the transaxle.

The speed and distance signals, along with a closed throttle signal from the TPS, determine if a closed throttle deceleration or normal idle condition (vehicle stopped) exists. Under deceleration conditions, the PCM adjusts the idle air control motor to maintain a desired MAP value. Under idle conditions, the PCM adjusts the idle air control motor to maintain a desired engine speed.

Vehicle Speed Signal Manual Transaxles

The vehicle speed sensor is located in the transmission extension housing on M/T vehicles. The sensor input is used by the PCM to determine vehicle speed and distance traveled and is a Hall-effect sensor.

The Hall-effect sensor generates 8 pulses per sensor revolution. These signals, in conjunction with a closed throttle signal from the throttle position sensor, indicate a closed throttle deceleration to the PCM. Under deceleration conditions, the PCM adjusts the Idle Air Control (IAC) motor to maintain a desired MAP value.

Like all Hall-effect sensors, the electronics of the sensor needs a power source. This power source is provided by the PCM. The sensor switches a 5-volt signal sent from the PCM from a ground to an open circuit. It is the same 9-volt power supply that is used by the CKP and CMP sensors.

When the vehicle is stopped at idle, a closed throttle signal is received by the PCM (but a speed sensor signal is not received) Under idle conditions, the PCM adjusts the IAC motor to maintain a desired engine speed.

The vehicle speed sensor signal is also used to operate the following functions or systems:

Speed control
Daytime Running Lights (Canadian Vehicles only)

The VSS used on 3-speed automatic and manual transaxle vehicles. A pinion gear that is meshed with the right axle drive shaft mechanically drives this sensor. When the PCM counts 4000 pulses, the PCM assumes the vehicle has traveled one mile.

Diagnosis & Testing

Checking For Diagnostic Codes

When trying to verify a speed control system electronic malfunction: Connect a DRB scan tool if available to the data link connector. The connector is located at left side of the steering column, and at lower edge of the panel.

A speed control malfunction may occur without a diagnostic code being indicated.

For further information and usage of the scan tool and a more complete list of Diagnostic Trouble Code and No Trouble Codes, refer to the section on DIAGNOSTIC TROUBLE CODES.

Road Test

Perform a vehicle road test to verify reports of speed control system malfunction. The road test should include attention to the speedometer. Speedometer operation should be smooth and without flutter at all speeds.

Flutter in the speedometer indicates a problem that might cause surging in the speed control system. The cause of any speedometer problems should be corrected before proceeding.

If a road test verifies a surge following a set, or an inoperative system, and the speedometer operates properly, check for:

A Diagnostic Trouble Code (DTC) If a DTC exists, conduct tests per the Powertrain Diagnostic Procedures service manual.
A misadjusted brake (stop) lamp switch. This could also cause an intermittent problem.
Loose or corroded electrical connections at the servo. Corrosion should be removed from electrical terminals and a light coating of multipurpose grease applied.
Leaking vacuum reservoir.
Loose or leaking vacuum hoses or connections.
Defective one-way vacuum check valve.
Secure attachment at both ends of the speed control servo cable.
Smooth operation of throttle linkage and throttle body air valve.
Conduct electrical test at PCM.
Failed speed control servo. Do the servo vacuum test.

When probing for voltage or continuity at electrical connectors, care must be taken not to damage connector, terminals or seals. If these components are damaged, intermittent or complete system failure may occur.

Removal & Installation


  1. Remove the air cleaner lid; disconnect the inlet air temperature sensor and makeup air hose.
  3. Remove the negative battery cable.
  5. Turn off ignition.
  7. Remove air bag.
  9. Remove the top mounting screw.
  11. Rotate steering wheel so that the switch is in the 6 oclock position. Remove 2 screws from the backside of the speed control switch.
  13. Disconnect the electrical connector.
  15. Remove switch.

To install:

  1. Connect the electrical connector.
  3. Install switch and tighten the screws to 1.6 Nm (15 inch lbs.) Make sure rubber seal is in place around switch.
  5. Install airbag.
  7. Install the negative battery cable.
  9. Install the air cleaner lid, connect the inlet air temperature sensor and makeup air hose.