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Coolant Temperature Sensor Replacing & Testing
 
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Pelican Technical Article:

Coolant Temperature Sensor Replacing & Testing

Nick Czerula

Time:

2 hours2 hrs

Tab:

$50

Talent:

****

Tools:

11mm, 13mm Socket, 22mm wrench, flathead screwdriver, digital multi-meter, jumper wires

Applicable Models:

BMW Z3 (1996-02)

Parts Required:

Engine coolant sensor

Hot Tip:

Work with a cool engine.

Performance Gain:

Remedy a check engine light or incorrect engine temp gauge

Complementary Modification:

Replace coolant at same time

The digital motor electronics (DME) engine management system in BMW Z3 vehicles receives input signals from a variety of sensors in order to meter fuel and regulate ignition timing. The most important sensors are as follows:

  • Mass air flow (MAF) sensor ahead of the air filter housing detect the mass and temperature of air entering the intake.
  • Engine coolant temperature (ECT) sensor detects coolant temperature at the cylinder head.
  • Crankshaft position (CKP) sensor detects crankshaft TDC position.
  • Camshaft position (CMP) sensor(s) detect cylinder firing position as well as camshaft timing advance or retard.
  • Engine knock sensor(s) detect pre-ignition or detonation.
  • Oxygen sensors detect oxygen content (and therefore engine combustion efficiency) in the exhaust stream.
  • Radiator outlet hose coolant temperature sensor detect the temperature of coolant leaving the bottom of the radiator.

The engine coolant temperature (ECT) sensor is responsible for sending the temperature of the engine to the DME and the instrument cluster. It is a four wire sensor, with two separate circuits, one for the instrument cluster and one for the DME. If you have a coolant sensor fault code stored in your DME and your engine isnâÂt running right, I suggest replacing the sensor before digging too deep. You may also have an inaccurate temperature gauge in your instrument cluster.

To avoid marring the paint and trim, work with a plastic prying tool or wrap a screwdriver tip with masking tape before prying out body or interior items.

Keep in mind that when your car was serviced before, parts may have been replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have, so be prepared with different size sockets and wrenches. 

Do not open the coolant reservoir cap or disconnect any coolant hoses or other components until the engine is completely cooled off. Hot coolant scalds.

When performing electrical tests, be sure to use a digital instrument such as a DVOM. Using an analog device may lead to damage to sensitive electronic components.

Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If you're working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Do not work on your vehicle if you feel the task is beyond your ability. 

Vehicle models change and evolve, as they grow older, so the vehicle shown in our illustrations may vary slightly from yours. If something seems different, let us know and share your info to help other users. Do you have questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.

In this article, IÂ'll go over the steps involved with replacing and testing the engine coolant temp sensor on BMW Z3 4-cylinder models.
Figure 1

In this article, IÂÂ'll go over the steps involved with replacing and testing the engine coolant temp sensor on BMW Z3 4-cylinder models. Be sure to work with a cool engine. The coolant temp sensor is located at the front of cylinder head on the left side (green arrow).

Replacing Coolant Sensor:

 Place a drain pan under the left front of your engine. You can drain the coolant. However I find very little leaks out during the procedure.
Working at front of the cylinder head, remove one 11mm fasteners (yellow arrow) and two 13mm fasteners (green arrows).
Figure 2

Working at front of the cylinder head, remove one 11mm fasteners (yellow arrow) and two 13mm fasteners (green arrows).

Once the fasteners are removed, remove the bracket.
Figure 3

Once the fasteners are removed, remove the bracket. You now have better access to the coolant temp sensor.

Then, disconnect the sensor electrical connector by pulling it straight off the sensor (green arrow).
Figure 4

Then, disconnect the sensor electrical connector by pulling it straight off the sensor (green arrow). The connector is held on by two small tabs. If they will not release, use a small flathead screwdriver to release them.

Now you can loosen the sensor.
Figure 5

Now you can loosen the sensor. Use a 22mm open end wrench and loosen the sensor about a half turn. This should be enough to remove it by hand the remainder of the way. Unscrew the sensor and remove it from the engine.

Be sure to replace the metal sealing gasket (green arrow) when replacing the sensor.
Figure 6

Be sure to replace the metal sealing gasket (green arrow) when replacing the sensor. Install new sensor finger tight. Then tighten it using an open end wrench. Be careful, it is easy to over-tighten the sensor. Top up and bleed cooling system. Then reassemble engine bracket.

Testing Coolant Temp Sensor:

I am going to show you a few quick ways to test the coolant temp sensor using a scan tool, the instrument cluster and a digital multi-meter. Be careful not to short any wires or damage electrical terminals during testing. Using the steps mentioned earlier, disconnect the coolant temp sensor.
This photo shows the coolant sensor electrical pins.
Figure 7

This photo shows the coolant sensor electrical pins. To test the sensor, connect your volt meter across two of the terminals and take a resistance reading. At 60f you should have about 6.5k Ohms between terminals 1 & 2 and about 2.5k Ohms between terminals 3 &4. Now insert the sensor into warm water, as the temp increases, resistance should decrease. Keep in mind, these are rough specs. I rarely test coolant sensors this way, mostly because they are either shorted or have an intermittent connection. I prefer to test the circuits back to the monitoring devices, if the circuits are good, I will replace the sensor.

This photo shows the location of the electrical connector terminal pin assignments.
Figure 8

This photo shows the location of the electrical connector terminal pin assignments. Green arrow points to pin 1. Yellow arrow points to pin 2. Red arrow points to pin 3 and the blue arrow points to pin 4.

Jump Pin 1 and Pin 2 together while monitoring the instrument cluster.
Figure 9

Jump Pin 1 and Pin 2 together while monitoring the instrument cluster. When the circuit is open, the temp gauge will read cold. When you jump the terminals together the temp gauge will read hot.

You can also test the voltage from the cluster to the sensor.
Figure 10

You can also test the voltage from the cluster to the sensor. Pin 1 should have about 3.5 volts. Pin 2 should have about 0.1 volts.

Jumping Pin 3 and Pin 4 together wonÂ't net the same results.
Figure 11

Jumping Pin 3 and Pin 4 together won't net the same results. Once a fault is set in the DME I find the scan tool will not display a temp value when the circuit is jumped. The key here is to check the scan data. Does the temp display -41c? If so, the DME sees an open circuit.

You can also test the voltage from the DME to the sensor.
Figure 12

You can also test the voltage from the DME to the sensor. Pin 3 should have about 5 volts. Pin 4 should have about 0.1 volts.

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Comments and Suggestions:
Laurence Comments: Hey there, this seems like an excellent tutorial. I have a 1.9 4 cylinder 2002 z3, right hand drive. Having removed the figure 3 bracket, there doesn't seem to be any sign of the temp sensor. I'm pretty confused now and worried that it's probably somewhere deeper down or in the jumble of hoses at the front of the engine. See attached picture. Any advice would be most appreciared! Thank you, Laurence
June 3, 2016
  Followup from the Pelican Staff: It should be there, however your engine may be different. This article applies to US models. - Nick at Pelican Parts  
henry Comments: have a 98 318i and i check voltage on harness for ect in pins 1 and 2 and i get the opposite voltage than what you explained. on pin 2 i get about 3.5v and on pin 1 i get about 1v. is there something wrong with this? pins 3 and 4 are fine
May 20, 2016
  Followup from the Pelican Staff: Your vehicle may be different, this article is for a Z3, your is a 318i. I would get a wiring diagram for your vehicle to confirm this data. - Nick at Pelican Parts  
Henry Comments: Where is the black lead going in step 10?
March 6, 2015
  Followup from the Pelican Staff: Battery negative. - Nick at Pelican Parts  
Brad Comments: I think my terminology is incorrect Nick, by OBC I mean the car computer, which is usually reset when required, by the external OBD diagnostics computer/scanner. sorry for confusion
January 14, 2015
  Followup from the Pelican Staff: No problem. - Nick at Pelican Parts  
Brad Comments: Thanks Nick, Does the OBC need to be reset after changing the coolant temperature sensor that feeds the DME if the engine was started with the sensor unplugged? The faulty sensor did not trigger a fault code, but was deemed to be faulty by a -40 odd degrees running temperature reading detected by the external diagnostics computer
January 14, 2015
  Followup from the Pelican Staff: I don't believe so. - Nick at Pelican Parts  
Brad Comments: Hi,

Does the e36 328i also only have one sensor, or are there two, one for the instrument cluster and one for the DME. The diagnostics computer reported engine temp to be -40 odd degrees, and I was told that there are two, but I can only see one, if I look through the inlet manifold, between inlet 1 and inlet 2. Thanks
January 13, 2015
  Followup from the Pelican Staff: There are a few. Two mounted in the cylinder head, the most forward one is for the DME, the one right behind it, for the cluster. - Nick at Pelican Parts  
zack abear Comments: For starters I have a 1998 323is m52b25 with software tuning and a couple other mode. I have a dead coolant gauge which occurred after replacing the bulbs in the cluster and doing a dme tune swap. It first pegged hot and then went cold and after it did that about three times it sits dead below cold now. All other gauges work fine. I have a diagnostics issue with the cars obdII system and can only periodically pull codes from it but have never seen a code surrounding coolant issues the car runs cool. I was considering replacing with an aftermarket aem coolant gauge for more accurate readings but if I pull this sensor to replace with the aem sensor will I experience engine issues such as dme fault codes? Thanks I love you guys for making this website
October 27, 2014
  Followup from the Pelican Staff: If you have a fault code, I would address it before replacing anything. If the gauge died after the repair, you may have damaged it. You can replace the cluster. - Nick at Pelican Parts  

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