# BOSCH Coolant Temp Sensor Data -Comprehensive CTS (ECU/Gauge and pinouts) - ABA, Corrado, 1.8T s



## sdezego (Apr 23, 2004)

That should help folks searching on titles..
Here it goes. I have read a lot of talk about different sensors and had some recommendations, but I wanted to verify the data for myself to provide different options to sensors, sensor plugs (harnesses) etc, etc.
I was looking for a 4pin sensor (2 sensors in 1 ECU/Gauge) for my Corrado switch to Megasquirt and ultimately 2L20v. The corrado uses 2 separate sensors stock (Blue CTS = ECU, Black CTS = Gauge). Since the 1.8T coolant flange has provisions for only one sensor and I wanted to use a 2 in 1 sensor, I decided to investigate.
Going into this, I was told all of the ECU Temp vs. Resistance curves are the same but that the gauge senders differ.
Veedubgti suggested that the ABA 4 Pin sensor is the correct one to use for both ECU and Gauge (corrado or other Mk2 cluster) and will prevent the temp gauge from sky rocketing and being incorrect at operating temp here -> 1.8t coolant temp with 8v cluster 
Since I had pretty much all sensors on hand I decided to calibrate them and check them against the values in EasyTherm for MS.
--------------- THE TESTS --------------------
I took 4 sensors, a pot of Ice water to start, a Thermocouple along with a thermometer, an Ohm Meter and a few







s
I logged temp vs resistance (about every 5*F) from 32*F - ~212*F
I just got done plotting them (1 for ECU and 1 for Temp Gage) out and here is what I found:
There is no significant difference with ANY VW sensors between ECU sensors and only very slight differences between Gauge Sensors. My ECU sensor data also corresponds directly with the Blue Corrado CTS from the Bentley (Shown below) as well as the value pairs in EasyTherm.
Here is what I tested (ECU pins and Gauge pins is applicable):

Corrado Black (Gauge) sensor.
AEB (Passat Blue) 4 pin sensor
ABA (Yellow Ring) 4 pin sensor (pictured above)
AWP (Late 20v Green) 4 pin Sensor
Initially it did not look like the small differences in temp vs resistance would have a noticeable effect the cluster's temp Gauge, but you will see below that was not the case.
-------- CLICK TO ENLARGE IMAGES ------------------
------------ The Setup --------------------------------



------------ SENSOR PINOUT and POSITIONS ------
 
--------------- THE ECU PIN DATA --------------------
 

--------------- THE GAUGE PIN DATA FULL ----------

 
---- THE GAUGE PIN DATA at OPERATING RANGE ---

 
You can see that at operating range the resistance is pretty small to begin with and there are differences in the sensors. As you can imagine, this does screw up the gauge readings as was originally suggested.
There are fixes though in case you really need/want to use a different sensor.

Forgot to ass the Stock Bosch ECU CTS Curve:











_Modified by sdezego at 7:09 PM 12-14-2006_


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## sdezego (Apr 23, 2004)

*Re: BOSCH Coolant Temp Sensor Data -Comprehensive CTS (ECU/Gauge and pinouts) - AB ... (sdezego)*


_Quote, originally posted by *fast-forward* »_I install TDIs into Vanagons. The ALH and BEW TDIs (1999 and later TDI) do exactly what you are describing to the Vanagon's temperature gauge. When you are at 93C operating temperature (measured with VAG-COM) the OE gauge feels the engine is too hot and the little LED will start to blink. If you place a 100 ohm resistor in line, the OE gauge goes very close to where it should be - this is the case at least for Vanagons and the MK-II Golf / Jetta.
Prost!










I just installed the Blue AEB one just for giggles and tested it out. Sure enough, it did act a little strange as described. In looking at the range near operating temps, it is off from the Corrado Black one, but the ABA is off as well.
It appears that the gauge is very sensitive around this area where small changes in resistance can affect the temp by say 15-20 degrees.
For example: at 172*F the resistance is:
PG - ABA - AWP - AEB
171 - 198 - 183 - 187 (ohms)

You can see that the AWP is the closest and the AEB is next, but based on the values that I see on the Gauge in the car (~ +15*F), I am agreeing that a small resistor might be perfect, but I can not explain why yet.
I am going to try the ABA as was recommended and might even try the resistor as well.

NOTE: I am not trying to re-invent the wheel here, just trying to find options for folks out there. The late AWP sensor is also about 1/2 the price of the ABA one. Still pretty cheap in relative terms though.
Shawn


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## sdezego (Apr 23, 2004)

*Re: BOSCH Coolant Temp Sensor Data -Comprehensive CTS (sdezego)*

ok, I didn't try the resistor on the Blue AEB and just tried the Late Green 20v AWP one that I had.
It was worse and the gauge went all the way up at operating temp and the light started blinking.
I then picked up a couple of various resistors, tried a few and settled on a 50-55ohm setup that works perfect in the Corrado to replace the Black sender.
I am still going to post all of the data for the various sensors, pin outs etc.
Also going to try the Yellow Ringed ABA one as suggested, but since the resistance if off from the Corrado, I am not sure how that one will work w/o resistors. I'll check it out
Shawn


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## G-radoT (May 20, 2006)

*Re: BOSCH Coolant Temp Sensor Data -Comprehensive CTS (sdezego)*

Awsome info man. http://****************.com/smile/emthup.gif


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## Salsa GTI (Aug 29, 2000)

*Re: BOSCH Coolant Temp Sensor Data -Comprehensive CTS (sdezego)*

Great info...I have some Megasquirt projects ahead..this will help


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## Veedubgti (Mar 5, 2001)

*Re: BOSCH Coolant Temp Sensor Data -Comprehensive CTS (Salsa GTI)*

Good info, however it should be pointed out that you are using different gauges of wire on some of your test pieces. Different gauges of wire will provide varying/inaccurate ohm readings from sensor to sensor, no?










_Modified by Veedubgti at 1:04 PM 12-14-2006_


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## sdezego (Apr 23, 2004)

*Re: BOSCH Coolant Temp Sensor Data -Comprehensive CTS (Veedubgti)*


_Quote, originally posted by *Veedubgti* »_Good info, however it should be pointed out that you are using different gauges of wire on some of your test pieces. Different gauges of wire will provide varying/inaccurate ohm readings from sensor to sensor, no?

The copper wire resistance is negligible. You are talking less than .5ohm total resistance in the thin wires and barely less in the larger ones. 
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_Modified by sdezego at 9:14 PM 12-15-2006_


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## the kevin (Feb 12, 2004)

*Re: BOSCH Coolant Temp Sensor Data -Comprehensive CTS (sdezego)*

good info..


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## sdezego (Apr 23, 2004)

*Re: BOSCH Coolant Temp Sensor Data -Comprehensive CTS (sdezego)*


_Quote, originally posted by *sdezego* »_UPDATE: 
Sorry in my haste and moment of retardedness, I did not hook up the correct pins yesterday when I tried the ABA Sensor. I will recheck it today and report back and update the above info.

- The ABA *does* appear to be pretty close or correct for the Corrado Cluster Gauge, but I have no idea why after looking at the data.
The AEB and AWP ones give readings too high of about (50-60 and 90-100 *F respectively). 
- Green AWP with a 50-55ohm resistor is perfect.
- Blue AEB with <undetermined resistor> but likely a 25-40 ohm resistor should be perfect as well.

Shawn


_Modified by sdezego at 9:16 PM 12-15-2006_


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