1991 Lexus LS400 EGR Valve Temperature Sensor Replacement Cost

Exhaust gas recirculation systems transfer exhaust from the engine from the exhaust system to the intake manifold. This is in effort to reduce emissions by allowing a more complete burning of fuel and preventing the formation of harmful chemicals. For more efficient operation, some manufacturers program the engine control module (ECM) to use an EGR valve temperature sensor to control the operation of the EGR valve.

The EGR valve temperature sensor will constantly read engine exhaust temperatures to determine if operation of the EGR valve is correct or incorrect. This may be used in place of an EGR valve position sensor so the ECM can monitor if the valve has opened upon request. When the EGR valve is opened, the EGR temperature sensor is heated by hot exhaust gases flowing through the EGR valve. Upon being heated, the EGR temperature sensor will change resistance which creates a voltage change in the signal voltage to the ECM. The ECM will interpret the voltage received from the temperature sensor as the EGR valve being opened or closed.

When the EGR valve temperature sensor fails, the ECM will identify this failure by illuminating the check engine light and storing on-board diagnostic (OBD) fault codes referencing the EGR system or the EGR valve temperature sensor. If the temperature sensor is at fault, this will be the only symptom of the failure in most cases. The worst case scenario is the engine running slightly rough and a decrease in fuel mileage.

While not an emergency, this issue should be repaired at the earliest opportunity. Not only does excess fuel consumption increase the cost to drive, but the additional fuel being pumped into the catalytic converter can cause premature failure.

EGR temperature sensors do fail, and it is mostly due to carbon buildup. They are exposed to extreme heat, carbon, exhaust gases, and temperature fluctuations. This means that they are designed to stand up to most abuse, but over time will likely fail.

When diagnosing the EGR valve temperature sensor, the connector will be probed for reference voltage at the sensor, and the signal voltage will be checked for change to temperature. Alternatively, the sensor could be removed from the EGR system, and resistance across the sensor could be monitored as the sensor is heated and cooled. It is important to understand that a sticking or leaking EGR valve can cause the sensor to appear to work incorrectly, so operation of the EGR valve will be checked also.

Replacement tents to require removing one electrical connector before detaching the sensor. Installation is the reverse of removal, and any seals should be replaced.

These sensors may cease functioning properly due to carbon buildup. It is not advised to clean them with harsh chemicals or wire brushes. Returned failure is likely after decarbonizing the sensor, and leaks from the sensor are more likely. It is always the best practice to replace this sensor when coated with carbon.

Many manufacturers have different forms of soliciting feedback from the EGR system. This being the case, it is important to understand the type of EGR feedback component used on the vehicle being serviced. Also, the EGR system is nearly as hot as the exhaust system, especially if the engine has been running under heavy load or high engine speed. Wait at least thirty minutes to one hour before servicing the system, or just ensure the portion you are servicing is cool to the touch before proceeding.

This is not a difficult diagnosis or replacement. As long as the EGR system and computerized automotive circuits are understood, this can be done by anyone with a multimeter and a little time to spare. Ensuring proper workplace safety is vital, especially when working with a hot system, and the DIY mechanic should understand the specific range of voltage the EGR valve temperature sensor may send or receive.