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Cylinder Head Temperature Sensor - Upgrade for 84-89 Carreras

Pelican Technical Article:

Cylinder Head Temperature Sensor - Upgrade for 84-89 Carreras

Doug Suds


1 hour1 hr






Ohmmeter, floor jack, two jack stands, two wheel chocks, safety glasses, lug wrench, flathead screwdriver, wire cutters, deep metric sockets, metric socket set, metric wrench set, needle nose pliers, 4-inch socket extension,

Applicable Models:

Porsche 911 (1984-89)

Parts Required:

Cylinder head temperature sensor

Performance Gain:

Less chance that you warp your cylinder head or blow the head gasket

Complementary Modification:

Replace the DME relay

The cylinder head temperature sensor measures the temp from cylinder head #3 and sends it to the DME computer. The original part (911.606.405.00) got its ground from the cylinder head and had a single wire going to the DME. Apparently this method of providing ground is unreliable, so the updated part provides its ground from a second wire (964.606.405.00 though there may be a new part number which is 930.606.915.00). Interestingly, on my car (87 Carrera), there already was a second ground wire in the car (two wires running to a 2-pin connector), even though the original sensor had only one wire (1-pin connector) and didn't use the ground. This was good news, because it meant that the upgrade didn't require any new wiring.

On the left side of the engine compartment towards the back, you'll see a bracket with three wire connectors on it, the top one is for the head temp sensor. If you try disconnecting the sensor while the car is running, you'll see that it does run but very roughly (and overly rich). I have heard some differing opinions on whether a faulty sensor could cause no-start conditions, but my car it definitely will not start with the sensor unplugged. It's easy to check if you have the upgraded (964-style) part in case you're wondering.

If you disconnect the sensor at the bracket in the engine tin, you'll notice that the left side (wire to DME) has two wires going to a 2-pin connector. The right side (wire to sensor) has a 1-pin connector if it's the original part (911.606.405.00), or a 2-pin connector it's the upgraded part (964.606.405.00). The upgraded part also has a thicker wire going to the sensor because it's really two wires (additional one for ground) under the insulation instead of the single wire on the original part. [Rumor has it that this is not actually a 962 part, but a 930 part instead.]

If you are diagnosing a no-start condition and have the original sensor, you might want to test the sensor's resistance to ground with an ohmmeter. Put the positive probe on the single pin in the connector coming from the sensor (the connector on the right which is fixed to the bracket) and the negative probe on a known good ground. If the sensor is working properly, it should read in the 1-2k ohms range. If it reads zero or infinity the sensor is probably bad. Interestingly, I can't seem to get a proper resistance reading from the new sensor, but it definitely works.

Okay, here's the procedure for upgrading the sensor without using any special tools. Jack up the car (rear) and secure it on jack stands, remove the left rear wheel. Inside the wheel well you'll see an oval-shaped grommet in the engine tin with a wire coming out, then the wire runs through another grommet up higher in the wheel well (along with two other wires). Remove the lower grommet by prying it out with a screwdriver. You'll see the head temp sensor in cylinder head #3 inside the hole in the engine tin. Normally a special tool would be required to remove and replace the sensor (a slotted socket that fits over the wire), but it's not needed.

Instead, cut the wire off the old sensor (as close as possible to the sensor itself), then extract the old sensor with a deep socket. Thread the new sensor in by hand and tighten it with some needle nose pliers (it's a bitch to get in there but works). Now pry out the top grommet with a screwdriver (this was very difficult, I actually had to cut out my old one). Feed the new wire through the bracket inside the wheel well (you'll need to remove and replace the little bracket). You'll notice that there are two additional wires that run through the top grommet (back into the engine compartment) along with the head temp sensor wire. Fortunately, the new grommet is slotted so these extra wires slip in easy. Slip the two extra wires into the new grommet and feed the wire through the hole. Don't replace the grommet till you've installed the wire in the engine compartment.

You should be able to reach into the back of the engine compartment and grab the new sensor wire. You'll see that it runs around the manifold pipes and through a bracket in the middle of the engine. This bracket can be easily removed with a 4" socket extension and wrench to feed the new wire through. To install the new wire on the bracket at the left side of the engine compartment, you need to take apart the bracket. You'll notice that there are two little screws on the face of the bracket. Remove these screws and the bracket slides apart. It's easier to get at these screws if you unplug all three wires (be sure to label them appropriately). Slide the old plug out, the new one in, replace the cover of the bracket.

You should see two pins in the connector on the DME end (left side). The top pin is for the temp signal, and the bottom pin is for ground. You may want to check that you are in fact getting a proper ground by reading the bottom pin with an ohmmeter. You'll notice that the connector on the sensor end (right side in the bracket) now has two pins instead of the original single pin. To complete the job, don't forget to reinstall the top grommet in the wheel well. This part is difficult, so be prepared to let a few profanities fly ;-)

That's it, head temp sensor 101, for the DIY mechanic. Thanks to Darrin Sacks for explaining how to do this with no special tools.

Doug (87 Carrera Targa)

Comments and Suggestions:
Leigh Comments: Wondering if the cylinder sensor is bad on my 1984 911? This has happened the last two times I have driven the car. Drove 20 miles, stop and shut the engine off, and the car sits for 30 minutes to an hour. I then start the car and idle for about 5 seconds, but then shuts off. Then it won't start or even fire, just turns over and over. Several hours later 2 to 5 the engine will start, but it runs very rough with some light backfiring. Pushing the accelerator makes no difference in the RPMs. I wait until the next day, and the car now starts and runs normally down the road. Ideas?
July 11, 2017
  Followup from the Pelican Staff: Could be many things. If running, I doubt the sensor is faulty. More likely a fuel delivery or air issue. - Nick at Pelican Parts  
Boots Comments: My 1987 cab ran great when hot and cold, but terrible when warm idle surged frantically until it warmed up. Replaced the CHTS and it runs perfect. Tip: just splice the new CHTS wire into the new one therefore avoiding needing to reach the difficult to reach upper grommet Be sure and get the wires right as they both look the same - I think this matters. Testing the old one and then the new one in a pot of hot water gave me exactly the same readings on my ohm meter. So don't test it just replace it.
May 12, 2017
  Followup from the Pelican Staff: Thanks for sharing your repair process and experience. These type of comments add so much to the Pelican tech community.
- Nick at Pelican Parts
85Targa Comments: My issue seems to be with the female end of the CHT sensor left side. My engine starts but when I wiggle the left side of the CHT sensor wire, the engine shuts down. I removed the rubber boot and peeled back the brown wire housing revealing a red/black power and a brown ground. I was expecting to see a break in the wiring. The copper wiring all looks good.

How can I replace the entire female end left side?
January 3, 2016
  Followup from the Pelican Staff: You will need a repair harness. That would be the individual terminals and the plastic connector. Give our parts specialists a call at 1-310-626-8765 - Nick at Pelican Parts  
switcher Comments: I had an intermittent cut-out problem with the engine on my 87. Replacement of the CHT sensor even though resistance was showing ok when measured solved the issue.
February 23, 2012
  Followup from the Pelican Staff: Thanks for the additional Info. We appreciate it.
- Nick at Pelican Parts
boots Comments: i have a 1987 911 cab. ever since the engine rebuild it starts great and runs GREAT and normally idles at 800 rpm. however, sometimes it idles at 1100 rpm and sometimes the idle surges from 1000 to 1300 for a few minutes then usually settles down. have replaced idle control valve and O2 sensor and have assured that the closed throttle micro switch is closed at idle. always rus good after an overnight cold start. any ideas about the surging?
May 18, 2011
  Followup from the Pelican Staff: Surging is usually a lean condition. Add fuel (carb spray or propane) and see if the idle continues to go up, if yes you have unmeasured air getting into the intake. What is the voltage on the idle speed motor when this happens? Is the computer reving the engine higher because it thinks the engine is colder than it is? - Kerry at Pelican Parts  
g8keapor Comments: I have a 993 and in the 993 case this is blocked by what looks like something related to the camshaft. you have to cur the wire or you can take a socket notch it then cut in half and weld the end to a flat piece of metal. it is kind of archaic but it works if you don't want to cut the wire. as for me well I have a welder but seeing as I already bought the sensor for like 75 bucks i really can care less what the old one reads out as swapping it either fixes this or it doesn't besides after 15 years its due for a new sensor anyway. clip went the wire
February 6, 2011
  Followup from the Pelican Staff: Thanks for the additional Info. We appreciate it.
- Nick at Pelican Parts
Chris. Comments: Question before I dig into this project:
What is the "correct" tool to use for removal? Is it possible to feed the wires through a socket without needing to cut the wire off? Would be great to confirm resistance of existing sensor - so as to know whether this was the root of my rough running engine.

October 20, 2010
  Followup from the Pelican Staff: You can also use a crowfoot wrench which will allow you to remove / install the sensor without having to cut the wire. The crowfoot is a bit more difficult to use than a regular socket though. - Wayne at Pelican Parts  
porschedc Comments: Hi i have a 2.7 with a 3.2 injection system and a Megasquirt ECU..My problem is i have no cold start sensor on the 2.7..can i adapt an aftermarket system without having to remove the engine..Paul
October 9, 2010
  Followup from the Pelican Staff: I think you can. I would contact the folks at meagsquirt to be sure. There's a bunch of info here: - Nick at Pelican Parts  
Ken Comments: I own a 87 Carrera Targa and I'm getting ready to change the cylinder head temp sensor. I read your tech article and was wondering it you had photos or know where I can find photos to go with the article. I'm would like a photo of where the grommets are located in the wheel well.
Ken87 Carrera Targa
November 8, 2009
  Followup from the Pelican Staff: It's super easy. If you search the forums (, I think there are some photos posted there. - Wayne at Pelican Parts  
jose Comments: the problem right now is different, I start the engine cold its OK... no engine stops, but when the car going hot and restart the car... dont start... then I disconect the head sensor and reconect again, then the car star good and I can go to gas station, or any place and I dont have start problem again... this is why I think the problem is the compu.. what you think?
August 24, 2009
  Followup from the Pelican Staff: Power to the DME is off when the ignition is off, so disconnecting and reconnecting the head temp sensor should not make a difference. If this is repeatable, my only guess is that there may be a fault somewhere in the wire harness? - Wayne at Pelican Parts  
jose Comments: thanks, I measure the ohms and read 1.8 in cold engine and 1.2 in hot engine... Its posibble reset the compu? 911 3.2 86?.. maybe my problem is the compu...
August 24, 2009
  Followup from the Pelican Staff: You can try to disconnect the battery and let it sit for 24 hours to discharge the system. This may reset it. - Nick at Pelican Parts  
jose Comments: hello. I have a start problems with my 911 3.2 86, when I disconnect the head temp sensor from the bracket, the car starts in idle hi rpms about 2000, when the car is cold, the engine starts, but begin warm .. the engine stops.. how I can see if the sensor its ok. before chance, I think the problem is a DME relay and I change and the problem its the same
August 2, 2009
  Followup from the Pelican Staff: You can take the sensor out and test it by dropping it in boiling water and measuring the rise. I believe the values are somewhere in a thread on our forums. - Wayne at Pelican Parts  

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Page last updated: Mon 1/22/2018 02:19:15 AM