# 98 VW Beetle TDI blue temperature sensor upgrade



## mobilni (Mar 31, 2010)

Hello,

98 TDI ALH New Beetle - temperature sender upgrade.
I have blue light flashing on dashboard, so it is time for another sensor.
In car is blue square sensor 4 pins.
I like to use green version - new style in ALH.
Question is can this be replaced, and what pair of wires go to instrument
cluster and what pair of wires go to ECM. 

Can anybody help me out with this one.

Thank you.


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## billymade (Jan 29, 2008)

Cooling temp light modes: 

_Blue coolant light = engine cold
*Flashing blue coolant light = fault in the coolant monitoring system
*Flashing red coolant light = low on coolant
Steady red coolant light = engine overheating, pull over and stop engine IMMEDIATELY and do not run until the problem has been identified._

So, you might have a electrical/wiring harness issue related to your coolant temp sensor; typically, you will get a associated trouble code, as well. I had the same problem, in my case; the terminal wire at the plug, was broken off. I replaced the plug, terminal wires and installed a new coolant temp sensor, the problem went away, stayed away. I bought the wiring harness parts and sensor; from my local VW dealer. You can get a pigtail online: that comes with the plug, terminal wires already installed together (typically cheap chinese knock offs); because of my electrical problems, I went ahead and spent the extra money, on genuine vw parts. 

The plug and sensor type; has varied over the years, there is the smaller green style and then, a bigger type. I'm not aware, of anyone "upgrading"; to the different type but I would stick with the type that came with your vehicle. The "green" sensor, was originally black; if I remember correctly and they just improved, revised the design (thus, the color change; to reflect the revision of the design). I would assume, if the other type; had similar problems, that they revised that one as well (current ones; seem to be a blue color). I'm not convinced; that there would be any benefit, to changing over the plug/sensor, to the later or different style and they may not be compatible? 

You might want to test the wiring/plug and the sensor; to confirm, you diagnosis/fault. 

https://workshop-manuals.com/volksw...ection/with_manufacturers_scan_tool/page_537/

Based upon the service manual; there is a reason, for the bigger and smaller 4 pin, different coolant temp sensor: 

(big plug) Vehicles with 80-pin control module

(small plug) Vehicles with 121-pin control module

The 1998/99 New Beetle models were kind of odd balls; as they, sometimes, had parts from the Mark III platform and tended to have unique parts, compared to the later 2000 on New Beetle's, which were more specifically fully the Mark IV platform. 

I would keep it stock and don't modify a system, that it is designed for the ecu, that is noted above. _As the old saying goes: "if it ain't broke; don't fix it!"
_
Here is a video; that might be helpful, to understand, how the coolant temp sensors fail: 

https://www.youtube.com/watch?v=TwQ-2xp_TK4

I believe, this is the right coolant temp sensor; that you need, stick with high quality oem parts. In this case Mahle/Behr/Hella; would be oem for VW: (always check for correct parts by VIN # or confirm by looking at the part # on your old sensor): 

Mahle Behr Coolant Temperature Switch 059919501

https://www.google.com/search?q=199...ome..69i57.13337j0j4&sourceid=chrome&ie=UTF-8

For the new terminal ends; vw sells yellow "repair wires", that have factory crimped terminals on them (two terminals per wire) and so, you would need two wires, to replace all four terminals. There are small plug seals; inside the plug, so transfer them, over to the new wires/plug. I used heat shrink, adhesive lined butt connectors; to butt splice the new terminal wires into the wiring harness, in place, of the old ones and these seal out the environment, eliminating any corrosion, in the future. These type of butt connectors, can be bought; at most auto part stores or places like Walmart or home improvement stores, local hardware stores. 

Let us know, how your testing, troubleshooting and any needed repair turn out, we can go from there. :wave:


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## mobilni (Mar 31, 2010)

*Thank you very much*

for info, I am not lucky guy to have broken wire, it is sensor what is dead.
Reason what I like to switch to new style is to keep everything simple to
repair because I have to other ALH what have new style of sensor.
New style (green) have resistance on one side of sensor 930 Ohm (A-B) and 
other side (C-D) have 1680 Ohm on room temperature. 
I am trying to find out what is resistance value on blue sensor. 
If I get that I will be upgrading sensor to new style in case that value is same. 
Case is already same so that part is easy and connector part is only 4 wire. 
On Internet I am not able to find info about internal reading of sensor, so hoping 
that somebody have working blue sensor, to read me ohm value. 
In link you will see new style sensor, just need to find same for old blue one.
Delete everything beforehttps://ibb.co/Q9T4B5v
Thank you very much for replay. Regards


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## billymade (Jan 29, 2008)

Did you check the testing procedure and correct ohm specs; detailed in the linked to the service manual pages, above?

VW coolant sensor # 059919501; online they are listed for pretty cheap $8-$20, you might just go buy a new one and then, test the sensor, to get the ohm readings and be able to compare the two different types of sensors, if they will work the same, etc. 

https://www.google.com/search?
biw=...&ved=0ahUKEwjXxtn2ttDrAhWVaM0KHfkoBa4Q4dUDCAw

URO cheapie for $6 from Autozone: 

https://www.autozone.com/engine-man...o-000172/473936_283762_0&searchText=059919501


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## mobilni (Mar 31, 2010)

*But I am not in USA*

and can't get good deals like you guys. Cheaper is so far 66$ for
square one, and 25$ for new style. I have new style in my stock but
still looking for ohm reading. I think in my case only part what showing
temp in instrument cluster is bad, other part for ECM is god. I will try
this weekend take everything apart and see can I find solution.
Thank you very much for help , I appreciate it. 
Regards


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## billymade (Jan 29, 2008)

Where are you located? Are those VW dealer parts prices? :screwy:


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## mobilni (Mar 31, 2010)

*Hello,*

I am in Canada, and I didn't go to dealer, it is from Napa.
Today after research, I will disassembly everything and will
perform full testing from scratch again to try solve it before winter.
Will post my finding later. Regards


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## billymade (Jan 29, 2008)

NAPA, at least here in the USA; is one of the highest priced aftermarket auto parts supplier. You might call around for better pricing; ordering online, from sites like amazon, is another option. Every once in awhile, my local vw dealer; surprisingly, will have competitive pricing as well, on some parts.

https://www.amazon.ca/Engine-Coolan...ld=1&keywords=059919501&qid=1599311110&sr=8-1


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## mobilni (Mar 31, 2010)

*Yes you are right*

that is way better price, will look around for sure.
Still looking to switch to new green style round one to get
away from old blue one. Found some info on Internet.
We will see how will play out.
Regards


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## mobilni (Mar 31, 2010)

*Blue temperature Sensor resistence*

Hello,

I was able to measure value of blue Engine Coolant Temperature Sensor 078919501B.
At engine temperature 41 C reading on pins: 2-4 - 715 Ohm wires Lilac (4) Brown/White (2)
At same time reading on pins: 1-3 - 1358 Ohm wires Brown/Blue (1), Brown/Green (3).
Voltage on pin 3 is 5V DC and on Pin 4 is 4.24 without sensor.

As per Ohm reading of new green style sensor 059919501A and this old style looks like it is same
sensors in different case. If you like to use new sensor on old beetle, pin 4 of old sensor 
need to be connected to pin A, and pin 3 need to be connected to D, pin 2 on B, and
pin 1 to pin C. 
I am not sure that anybody will need this info, but you never know.


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## billymade (Jan 29, 2008)

Any updates? Did you fix the problem and how did the upgraded coolant temp sensor, work out for you?  :wave:


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## mobilni (Mar 31, 2010)

*Hello*

Sorry about delay, I have now different problem, to deal with
but Beetle working fine. Check my other post, maybe you can
help me with BEV engine.
Best Regards :banghead:


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## billymade (Jan 29, 2008)

Sorry, i don't know much about tdi's; when it comes to engine swaps with different era features and possible compatibility issues, sticking with the same parts, is typically the least hassle way to go. For more tdi specific advice; check out tdiclub.com


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## mobilni (Mar 31, 2010)

*Now we have*

gasoline engine what give me headache, so maybe you will be in better position.
Regards


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