01 325i Temp Gauge Jumps Up Then Back Down

Dan Ferrell writes about practice-it-yourself auto maintenance and repair. He has certifications in automation and command technology.

Most coolant temperature sensors resemble a big nut with an electrical connector on meridian.

Photo courtesy of l0lnix on Flickr.

The engine coolant temperature (ECT) sensor examination is unproblematic and can assist you lot fix your car faster. You tin can exercise it at home using a digital multimeter and a cooking thermometer. A bad engine coolant temperature sensor affects engine operation:

• It may cause a abiding lean air/fuel mixture, causing the engine to stall or idle crude.
• Or it may cause a abiding rich air/fuel mixture, causing an increase in emissions and fuel consumption.
• On modern vehicles, a bad ECT sensor volition upset ignition timing.
• On some vehicle models, a bad ECT sensor may upset the manual, cooling fan, and temperature gauge as well.

But before you blame the coolant temperature sensor for your engine problems, though, utilise this guide to exam the sensor to confirm that you really need to replace it. The exam only takes a few minutes.

• Digital multimeter
• Kitchen thermometer
• Wrench (ratchet and socket prepare, if yous need to remove components)
• Paper and pencil

Locate the Coolant Temperature Sensor

Open the hood of your vehicle to find the coolant sensor.

1. Depending on your particular vehicle model, y'all may observe the sensor mounted on the cylinder caput or intake manifold. Nevertheless, one of the most common locations is on or nearly the thermostat housing. Y'all tin can notice the thermostat housing by following the upper radiator hose, which connects to the thermostat housing on the engine side.
2. Look for a big nut with an electrical connector on peak, and two electric wires coming from the connector — on most mod vehicles — or i wire — on older vehicle models.
3. Some sensors are buried under the intake plenum, specially on large trucks, and you demand to remove the intake merely to proceeds access to it.

If yous still take problem locating the ECT sensor, consult your vehicle service manual. You can buy a service manual for your particular automobile brand and model in almost auto parts stores or online. Bank check the Amazon advert below.

Use a digital multimeter to exam your coolant temperature sensor.

Photo courtesy of Andy / Andrew Fogg on Flickr.

Coolant Temperature Sensor Test

Now that y'all've located the ECT sensor on your vehicle, y'all're prepare to troubleshoot it.

1. Unplug the sensor electrical connector.

ii. Become the engine surface temperature using an infrared thermometer or suitable cooking thermometer. Take the engine temperature on a location well-nigh the coolant temperature sensor.

Before going on to the next footstep, let's divert here for a second:

Okay, at this point you may be wondering why you need to take the engine temperature to troubleshoot the sensor. The main reason is that you are trying to check two common, potential failures here, the ECT sensor and the thermostat.

Allow's say that the thermostat on your vehicle got stuck in the open position. This will not allow the engine to reach operating temperature considering the coolant is flowing continuously. If y'all were to test the coolant temperature sensor alone, you may think that information technology failed because its resistance value has remained at nearly 1500 or 2100 ohms, for example, when in fact the sensor is reporting the coolant actual temperature and it's working properly.

Scroll to Continue

Read More from AxleAddict

Yous could relay on the temperature estimate on your dashboard. However, on some vehicle models this gauge works through the ECT sensor every bit well. Then, if the sensor doesn't piece of work properly, your temperature gauge won't exist of much help either.

By using the thermometer, it won't take you lot long to effigy out that the thermostat isn't working. You'll notice the engine's temperature is not rising to a higher place 85 or ninety degrees, for example.

On the other hand, if the thermostat works fine, the engine temperature volition reach near 200F (93C) and volition drib afterwards as the thermostat opens. Then you eliminate the thermostat every bit another possible failure.

Okay, at present let's become on to the next step.

three. Have a note of the temperature reading.

four. Now, using your ohmmeter, measure the resistance value of the coolant temperature sensor by hooking up one of the meter's leads to one of the terminals on the sensor electrical connector, and the other lead to the other terminal on the sensor electrical connector.

On vehicles with old, single-wire sensors, hook up the meter leads to the terminal on the connector and the sensor'southward body (ground) to accept your reading.

5. Cheque your vehicle service transmission for the correct resistance value for your ECT sensor. However, non all service manuals have this data.

Most sensors of this type have a resistance value of 3000 ohms or more at about 55F (13C). You may want to try searching online for a resistance value table for your item ECT sensor, if you know your sensor's brand.

However, whether yous find the resistance values for your particular ECT sensor, proceed with this tests anyway, the sensor'southward behavior and the temperature readings may give you lot a clue to its operating condition.

6. Make a note of the sensor'southward resistance.

Now y'all're going to take another pair of readings.

7. This time, commencement the engine and let information technology idle.

eight. Set the transmission to Neutral and apply the parking brakes.

ix. Look for about one to two minutes and measure the engine temperature and the sensor'southward resistance as you did before.

x. Brand a note of these new pair of values.

11. Without turning off the engine, wait for well-nigh one to two minutes and repeat this process again.

12. Take some other pair of readings in nearly i to two minutes again, always noting the value readings.

13. Then turn off the engine.

On the side by side video, you'll run across an alternative method to test a sensor using h2o. Of class yous need to remove the sensor from the vehicle to employ this method. However, the video will give you a visual reference well-nigh how to test your ECT sensor. Check it out.

Checking Your Readings

Now, compare your figures to the resistance and temperature ratings for your particular sensor listed in your vehicle service manual.

If you lot don't have the reference resistance values for your ECT sensor, brand sure that your sensor resistance readings decreased proportionally as the engine temperature increased. This will signal that your coolant sensor is responding to engine temperature.

Also, make sure the engine reached operating temperature at about 200F (93C) before dropping. If engine temperature didn't modify much throughout your readings, the thermostat is stuck open up and you need to supervene upon it.

When should you supersede the sensor?

• Whether you lot got an unusual reading or non, bank check that the wiring and electric connector is free of corrosion. If one or more wires bear witness sign of harm, repair them. Remove corrosion from the sensor's electric last using electrical contact cleaner and repeat your test, if necessary.
• If the ECT sensor'due south resistance didn't modify as the engine temperature rose, replace the sensor.
• If your sensor merely registers space resistance, the sensor has a cleaved internal contact and you demand to supervene upon it.
• If the sensor only registers zero resistance, the internal contacts are shorted. Replace the sensor.

The thermostat housing is one of the about common locations for a coolant temperature sensor.

Photo courtesy of Neb Abbott on Flickr.

The coolant temperature sensor test is rather simple. It merely takes a few minutes and you don't fifty-fifty take to remove the sensor from the engine for the troubleshooting procedure. Following the steps outlined in this guide will help you quickly determine whether you need to supplant the sensor and will also check the thermostat performance at the same fourth dimension by using a thermometer. Too, make sure to inspect the sensor electrical terminal for damage and corrosion, and cheque the circuit wires for possible damage. Information technology won't help that your ECT sensor tests Okay when it has to operate with a damaged terminal or wire.

Exam Your Knowledge of Declining ECT Sensors

For each question, choose the all-time reply. The reply key is below.

1. Which is Not a Symptom of a Potential Bad ECT Sensor
   • Continuous rich air-fuel mixture
   • Continuous lean air-fuel mixture
   • Rough idle
   • Engine misfire
   • Engine stalling
   • Increased emissions
   • Increased fuel consumption

Respond Key

1. Engine misfire

This article is accurate and truthful to the best of the writer'south knowledge. Content is for informational or amusement purposes just and does not substitute for personal counsel or professional person advice in business, financial, legal, or technical matters.

Questions & Answers

Question: I replaced my ETC and at present the guess reads hot, what could this be?

Reply: If the gauge goes all the way into cerise as before long as y'all plow the primal, there might exist a bad electrical connection - bank check the wires (damage) and connections at the ETC, but in some cases yous all the same need to look farther into the PCM or module, depending on your model. You may need to look the diagram for your model.

Question: I replaced the ECT twice. The temp gauge sticks all the way cold and fans are constant. It blows heat and doesn't overheat. As well, coolant is only warm to the touch when the engine has been running for an hour. Is my thermostat causing my temp sensor to go on declining?

Answer: There could be more than than 1 issue here. You lot may want to check the temperature sensor circuit and the sensor. You may need your vehicle repair transmission to trace the excursion in your particular model. Also, check the thermostat, if necessary. These two posts may assist.

https://axleaddict.com/auto-repair/car-thermostat-...

https://axleaddict.com/machine-repair/How-to-Supplant-...

Question: Why is there pressure return to the coolant reservoir, and coolant to hot, only the radiator fan still won't plow on?

Answer: Exam the temperature sensor. The fan tin can likewise neglect, and wires in the excursion can break or get loose. Cheque the connectors too.

Question: Why does temperature gauge go upwardly to only 130 and then drib back down continuously while the truck is started?

Respond: At that place could be a problem with the thermostat. Feel the radiator hoses while the engine is warming up and subsequently a few minutes and run across if the thermostat is opening.

Question: Why won't cooling fans appoint when the A/C is turned on and the clutch is not engaged?

Answer: The system may be low on refrigerant. Without pressure, the arrangement volition non generate oestrus so that the cooling fans won't come up on. There could be a problem in the circuit itself, perhaps on the high pressure level. Also, have the A/C system serviced.

Question: The reading from my coolant temperature sensor while plugged is different from the transmission self-cheque I did. Does this mean that I take a bad PCM?

Respond: Compare your reading to specifications, and exam both voltage and resistance, if possible. Practise a common cold and hot temp reading to double check.

Question: Will my ECT cause cool air to blow?

Respond: The problem could exist with the HVAC blend door. I would check the control unit or motor for the door.

Question: When idle, I've noticed the ECT climb upwardly to 235 degrees F and proceed. It starts going back down when I start moving again. How high can the engine get before it'southward not normal?

Reply: It depends on the model, just a skillful operating temperature ranges at 195-225, including modern engines. If the temperature climbs when idling, you may desire to cheque the coolant level, radiator fan and bulldoze chugalug. Usually, these are the ones the cause trouble at idle.

Question: When the ECT is bad, should the problem code definitely come up or not?

Reply: Ideally, this should be the case. But it may differ in certain models depending on the enable criteria ready for the computer. If the fault is within the electrical components or the circuit and the mistake but appears for a second or less then a second, the computer may not register the mistake, if not all conditions are met. This is also the case with some crankshaft position sensors on some models. In this case, you should look at the symptoms.

Question: What coolant temperature sensor do I use for a Daihatsu G200 car?

Answer: This video may give y'all an idea of the location:

https://www.youtube.com/lookout man?v=OoAiRt7hO14.

Question: Will it hurt my motor driving it if it goes straight to red?

Answer: Yes, it can damage the block, cylinder head, head gasket and can outcome in very expensive repairs. Attempt to pull off the route if temperature gauge goes straight to reddish and shut off the engine. Let it cool and run across if you can detect out the cause of the trouble or have your car towed to the garage.

Question: Can the coolant temperature sensor prevent a vehicle from starting?

Answer: It may cause a hard-to-commencement status or cause the engine to stall after starting, since the computer won't know to add together actress fuel for a cold start.

daniellestathe.blogspot.com

Source: https://axleaddict.com/auto-repair/Coolant-Temperature-Sensor-Test

Share this post