Author Topic: Temp sensor test (Read 1101 times)

Lbxpdx · « **on:** August 18, 2023, 08:22:28 PM »

92 K75rt

I’m changing fuel lines and decided to test my temp sensor. Pin 10 at room temp, around 85, it is measuring 3.5M ohms. It should roughly be 2.5k ohms, correct?

I have my meter set to auto and I keep getting 3.5m ohms.

Do I need to pull the sensor and heat it up in water to check it or should I just replace it?

Laitch · « **Reply #1 on:** August 18, 2023, 08:37:58 PM »

Quote from: Lbxpdx on August 18, 2023, 08:22:28 PM

Pin 10 at room temp, around 85, it is measuring 3.5M ohms. It should roughly be 2.5k ohms, correct?

What do the symbols M and k mean to you?

Lbxpdx · « **Reply #2 on:** August 18, 2023, 08:40:55 PM »

Doesn’t M means 1,000 K?

Laitch · « **Reply #3 on:** August 18, 2023, 08:50:03 PM »

Is that a question or is it an answer?

Lbxpdx · « **Reply #4 on:** August 18, 2023, 08:51:16 PM »

I was under the impression that M was megaohm, which is a 1,000x greater than K.

Laitch · « **Reply #5 on:** August 18, 2023, 08:58:59 PM »

What do you mean by an impression?

frankenduck · « **Reply #6 on:** August 18, 2023, 09:02:29 PM »

At 30C (86F) the resistance should be 1,707 ohms +/- 5%. (1.707 Kohms)

Where are you measuring the temp sensor resistance? Between the two terminals (wrong) or between each terminal and ground? (correct)

The K75/K100 temp sensor is a dual temp sensor the signals both the fan/thermo relay and L-Jetronic ECU.

Lbxpdx · « **Reply #7 on:** August 18, 2023, 09:02:48 PM »

Are you a college professor? I feel as though the Socratic method is being used on me to further my knowledge through actual understanding versus being told the answer.

Lbxpdx · « **Reply #8 on:** August 18, 2023, 09:04:50 PM »

I was checking at pin 10 to ground. When I checked the actual sensor to ground o got 2.23k.

Laitch · « **Reply #9 on:** August 18, 2023, 09:53:41 PM »

Knowledge through understanding isn't all bad; after all, I'm trying to understand you and I don't feel bad at all.

If you're confident that you understand how to operate a multimeter, that you are testing the correct control unit, and that you understand the function of the two pins on the temperature sensor, then the choices would seem clear. If test data at the fuel injection control unit does not conform to the standards from which you are working, you can confirm them by the boiling water method if that method is understood, or you can buy the correct model of coolant temperature sensor from a reliable vendor right now.

I'm going to have some hommus on sourdough then hit the hay.

frankenduck · « **Reply #10 on:** August 18, 2023, 10:02:21 PM »

How is your MPG and what do the spark plugs look like?

If the resistance is way higher then it should be then the L-Jet will overfuel, thus killing your MPG and foul the plugs a little.

frankenduck · « **Reply #11 on:** August 18, 2023, 10:50:59 PM »

FYI: If you do decide to replace the temp sensor then the Bosch part number is 0280130069. It's a pretty common temp sensor that was used on Volvos and Porches as well as K bikes.

Lbxpdx · « **Reply #12 on:** August 18, 2023, 10:55:42 PM »

Thanks for the info. I’ll check my parts as I may have one in my Volvo bits.

Lbxpdx · « **Reply #13 on:** August 19, 2023, 01:14:05 PM »

I’m going to pull the tank again and check the resistance across E and 31. If that checks good and I still get a funky reading at the ECU plug, does anyone know if there is a connector between the plug and the temp switch? I’m hoping there is and that it needs some DeOxit as the temp switch read fine when the plug was disconnected.

rbm · « **Reply #14 on:** August 19, 2023, 02:12:18 PM »

There is a four pin connector that joins the auxiliary harness to the main harness. The temp sensor wiring goes through that connector. It is located on the left side of the bike, near the air box just above the throttle bodies.

Lbxpdx · « **Reply #15 on:** August 19, 2023, 03:06:29 PM »

Thanks.

I feel like I’m doing something wrong, but here are my numbers.

On the male 4-pin connector I get 2.92k. What I feel is odd, is if I follow the male side it appears to go into the same harness as the motronic plug, though I get no reading at the 10 pin when the 4-pin connector is disconnected.

I get the same 2.92k at E to 31 on the relay.

On the female side of the 4 pin connector I get 4.51k when the relay is installed. I get 4.51k between E and 31 on the relay too. When I throw a jumper between E and 31, I get .06 ohm resistance.

I don’t know what the resistance should be on the relay.

The Mighty Gryphon · « **Reply #16 on:** August 19, 2023, 04:14:11 PM »

First of all, the four pin connector goes to the temperature relay. That side of the two sensors is only used to turn on the cooling fan. It has NOTHING to do with fuel mixtures going into the engine. For now, forget about it.

The only resistance you are interested in is the one going to the JETRONIC. (your bike does not have a Motronic control). Read that resistance on the JETRONIC plug between pins #10 and #13. If it reads higher than approximately 2500 ohms(2.5K) you need to get back to the sensor and clean the plug that connects to the sensor as well as the pins on the sensor. Then check the resistance again(at the JETRONIC plug, not the relay or the four pin plug that goes to the relay).

If the resistance is still wrong you need to change the sensor.

Lbxpdx · « **Reply #17 on:** August 19, 2023, 04:21:34 PM »

Ok, so I checked the plug yesterday, each side to ground and got 2.2K if I recall. When I check at pin 10 to ground, I get 3.5 M ohms. When I check pin 10 to pin 13 I get 10.8 M ohms.

The Mighty Gryphon · « **Reply #18 on:** August 19, 2023, 04:40:09 PM »

Are you talking about the plug at the sensor itself or the one that is going to the temperature relay? I'm having a hard time following what you are doing. I am an old man and my brain is beginning to fail. Please read what I have written slowly.

The sensor element that controls the mixture doesn't go to the connector for the relay, it goes directly to the Jetronic connector pin #10. If you are not reading the correct resistance at Pin #10 relative to pin #13 go to the sensor itself and pull the plug off of it. Then check the resistance from each of the pins on the temperature sensor referenced to ground on the frame. DO NOT measure the resistance between those two pins on the sensor. If the sensor is good, both of those pins should have nearly the same resistance relative to ground.

If the resistance at the temperature sensor is correct(about 2500 ohms), the problem is in the connector or the wire connecting the sensor to pin #10 at the Jetronic. Check the continuity between the temperature sensor plug and pin #10 at the Jetronic. One of the connections at the temperature sensor should show a very low resistance to pin #10. If neither contact on the temperature sensor plug shows continuity to the Jetronic pin #10, you have a problem in the plug or in the wire between the temperature sensor plug and the pin #10 on the Jetronic.

I hope this helps.

Laitch · « **Reply #19 on:** August 19, 2023, 04:43:24 PM »

When you get a chance, read the document at the link below. It explains your Brick's engine system.

The Mighty Gryphon · « **Reply #20 on:** August 19, 2023, 04:45:22 PM »

Are you sure you are reading the resistance at the correct pins on the Jetronic connector?

Lbxpdx · « **Reply #21 on:** August 19, 2023, 05:04:32 PM »

Thanks I will read that in a bit.

I pulled the wire off the temp sensor and it read 2.2K on each pin when grounded.

I checked and found continuity at pin 10 through the wire, resistance was 0.06.

I plugged the wire back into the temp sensor and again when I check pin 10, I get 3.5M ohms.

The Mighty Gryphon · « **Reply #22 on:** August 19, 2023, 05:09:38 PM »

Clean the connector for the temperature sensor. There is corrosion in it. This is a pretty common malady being where the sensor is located.

The Mighty Gryphon · « **Reply #23 on:** August 19, 2023, 05:13:25 PM »

Are you grounding your meter to pin #13 on the Jetronic plug?

Laitch · « **Reply #24 on:** August 19, 2023, 05:24:00 PM »

Quote from: Lbxpdx on August 19, 2023, 05:04:32 PM

I checked and found continuity at pin 10 through the wire, resistance was 0.06.
I plugged the wire back into the temp sensor and again when I check pin 10, I get 3.5M ohms.

Do you believe your probe in that photo is on pin # 10? If so, how do you reconcile that with the attached diagram from the K-model testing manual at this link?

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Author Topic: Temp sensor test (Read 1101 times)