exhaust gas temperature

What you need to know about Exhaust Gas Temperature Sensors and Oil Level Sensors

Cambiare explains the workings of two very diverse, yet important elements within the engine management system – Exhaust Gas Temperature Sensors (EGTS) and Oil Level Sensor.

Vehicle electronics specialist Cambiare understands the importance of introducing products that are relevant to the current aftermarket demands and regulatory requirements placed on modern engine systems. Two essential components within the engine management system are Exhaust Gas Temperature Sensors and Oil Level Sensors. Cambiare explains the importance of both elements-:

Exhaust Gas Temperature Sensors (EGTS)

With emission standards becoming increasingly stringent, vehicle manufacturers are developing newer technologies to meet the legislations necessitating the release of cleaner exhaust gases. An EGTS measures the temperature of the exhaust gas which is monitored by the Engine Control Unit (ECU) to help prevent damage to components.

Function

There are two variations of EGTS: Positive Temperature Coefficient (PTC) and Negative Temperature Coefficient (NTC) sensors. Typically measuring temperatures up to 900°C in the exhaust system, the resistance of the EGT sensing element alters with the change in exhaust temperature.

Whilst the more common PTC sensors function by increasing their resistance with increasing exhaust gas temperature, the NTC sensors decrease their resistance with a subsequent temperature increase. This resistance is registered by the ECU in order to take necessary actions, ranging from protection from thermal overload during Diesel Particulate Filter (DPF) regeneration and Selective Catalytic Reduction (SCR) to exhaust gas recirculation and overall engine combustion.

See below cross-section image through an EGTS:

Failure

A faulty sensor can drift out of tolerance limits and give incorrect readings, causing over-fuelling issues during regeneration, due to the process being prolonged. PTC EGTS are designed in such a way that it will continue to relay misinformation to the ECU without setting a diagnostic trouble code, making it seem like the DPF is regenerating within its permitted temperature range and delay the detection of thermal overload. Many a time, a DPF is wrongly assessed to be faulty, when it’s actually the failed EGTS which needs replacement.

NTC sensors, on the other hand, are designed with two wires bonded to a ceramic cell. With time, this bond can break and the sensor goes into an open circuit, triggering the engine check light – an easy fault to diagnose.

EGTS are primarily prone to damage during exhaust component replacements and should, therefore, be replaced simultaneously with a DPF and/or exhaust, rather than waiting for the dashboard warning light to illuminate.

Other causes include:

  • Severe vibration that can break the connection of internal wires.
  • Excessively high temperatures (T>900°C) causing resistance deviation of the thermistor element.
  • Severely bent wires (where bending diameter<20mm) that can cause wire breakage.
  • Contamination from oil, antifreeze or poor fuel quality.

Timely diagnosis and replacement of a defective EGTS prevents damage to the DPF and subsequent engine damage.

Oil Level Sensors

The oil level sensor plays a simple but critical part in the functioning of the engine.

Function

Its purpose is to monitor the engine oil level and alert the driver when it goes beyond acceptable limits. Not acting on the signal promptly could lead to significant engine damage and consequently, expensive repairs.

Whilst there are various kinds of oil level sensors, the latest technologies are seen in the Ultrasonic type. Ultrasonic sensors are transducers that convert ultrasound waves to electrical signals or vice versa. Essentially acting like microphones, they detect ultrasonic noise present under certain conditions, convert it to an electrical signal and relay this information back to the driver as dashboard warnings.

An oil level sensor warning light on the dashboard will light up when the engine is running low on oil. However, some vehicles have check control systems which warn the driver when the oil level is either too low or too high. See below graph illustrating vehicle oil level thresholds:

Replacement

The oil level sensor is mostly located on the sump and is fixed in place with three or four bolts and an electrical connector. Depending on its location, the replacement of the sensor can be quite straightforward. However, any residual oil should be drained before changing the sensor.

Warning Lights

If the dashboard warning light keeps illuminating or the oil gauge reads low even after a top-up, there is a good chance that the oil level sensor is faulty.

In such situations, the following steps are recommended:

  1. The oil level should be checked manually with a dipstick, wherever possible
  2. If the reading is full, the circuit should be tested for wiring defects
  3. The oil level sensor should only be replaced if found faulty and all other faults have been checked for

Cambiare's Offering

Cambiare’s current range of over 100 EGTS covers 2.6m vehicles in the UK and offer both variations: positive temperature coefficient (PTC) and negative temperature coefficient (NTC) sensors. Furthermore, Cambiare has introduced a range of 10 oil level sensors, covering 1.2 million vehicles on the UK roads. All parts are OE quality and each come with a 2 years/30,000 mile warranty. Speak to a local Cambiare or FPS representative for more information.

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