Technical Definition:

Brake Switch A / B Correlation

Technical Description:

Possible Causes:

• The most common is the brake light switch whose failure is due to wear.
• The brake light fuse will fail at times due to moisture in the circuit or burning out the brake light.
• Brake light bulb failure is another cause many times due to water infiltrating into the lens.
• The wiring harness, more specifically the connectors are loose or pushed out pins will cause a correlation problem between the switch and PCM.
• Lastly, the PCM itself could have failed.

Possible Symptoms:

• The brake lights will either be illuminated continuously or fail to illuminate as the pedal is depressed
• It will be difficult or impossible to shift out of park
• The vehicle may stall when the brakes are depressed while a cruising speeds
• The cruise control will not activate

Possible Solutions:

OBD-II Trouble Code Type:

Diagnostic Step:

Tech Notes:

Specific Makes:

Technical Definition:

Idle Air Control System

Technical Description:

Possible Causes:

• IAC motor connector is damaged
• One or more IAC circuits open or shorted to ground
• One or more IAC circuits are shorted to voltage
• IAC has failed
• PCM has failed

Possible Symptoms:

• MIL (Malfunction Indicator Lamp) illumination
• Engine stalls and may not idle unless throttle is depressed
• Intermittently stalls when letting off the throttle
• Engine may idle too high

Idle Control System Malfunction

Possible Solutions:

OBD-II Trouble Code Type:

Diagnostic Step:

Tech Notes:

– Faulty IACV-AAC valve
– IACV-AAC valve harness is open or shorted
– IACV-AAC valve circuit poor electrical connection

Specific Makes:

– Engine hard to start
– Rough or erratic idle speed

Technical Definition:

Idle Air Control System RPM Lower Than Expected

Technical Description:

Possible Causes:

Possible Symptoms:

Idle Control System RPM Lower Than Expected

Possible Solutions:

OBD-II Trouble Code Type:

Diagnostic Step:

Tech Notes:

– Dirty throttle body
– Electric throttle control actuator misadjusted or damaged
– Faulty Electric throttle control actuator
– Intake air leak
– Poor electrical connection to the Intake Air Control (IAC) valve

Specific Makes:

– Engine hard to start
– Rough or erratic idle speed

Technical Definition:

Vehicle Speed (Sensor A) Range / Performance

Technical Description:

Possible Causes:

Possible Symptoms:

Possible Solutions:

OBD-II Trouble Code Type:

Diagnostic Step:

Tech Notes:

Specific Makes:

Technical Definition:

Vehicle Speed (Sensor A) Circuit Low

Technical Description:

Possible Causes:

Possible Symptoms:

Possible Solutions:

OBD-II Trouble Code Type:

Diagnostic Step:

Tech Notes:

Specific Makes:

Technical Definition:

Vehicle Speed (Sensor A) Intermittent / Erratic / High

Technical Description:

Possible Causes:

Possible Symptoms:

Possible Solutions:

OBD-II Trouble Code Type:

Diagnostic Step:

Tech Notes:

Specific Makes:

Technical Definition:

Vehicle Speed Sensor A

Technical Description:

Possible Causes:

• The Vehicle Speed Sensor (VSS) is not reading (functioning) properly
• There is a broken/frayed wire leading to the vehicle speed sensor
• The vehicle’s PCM is not correctly configured for the actual tire size on the vehicle

Possible Symptoms:

• loss of anti-lock brakes
• the “anti-lock” or “brake” warning lamps on the dash may be lit
• the speedometer or odometer may not work properly (or at all)
• your vehicle’s RPM limiter may be decreased
• the shifting of an automatic transmission may become erratic
• other symptoms may also be present

Possible Solutions:

• The simplest thing to do is to reset the code and see if it comes back.
• Next, check all wiring and connectors that lead to the speed sensor. The location of the sensor depends on your vehicle. The sensor could be on the rear axle, transmission, or perhaps the wheel hub (brake) assembly.
• If the wiring and connectors are OK, then check the voltage at the speed sensor. Again, the exact procedure wil depend on your make and model of vehicle.
• If everything looks OK, replace the sensor.

OBD-II Trouble Code Type:

Diagnostic Step:

Tech Notes:

Specific Makes: