I believe it’s on the water crossover pipe under the intake. There are technically two coolant sensors. One is silverish with a single spade connector for the guage. The other should be brass with a plastic connector on it, that’s for the ECU.

 

Thanks, will have a look tomorrow

 

That engine should have but one coolant temperature sensor on the water (aka crossover) pipe with a two-wire, roughly oval-shaped connector.

The sensor resistance is inversely proportional to its temperature. The resistance is monitored by the ECM, which, in turn, uses the data for engine management, and sends data to a microprocessor in the instrument panel/cluster. The processor controls the warning lights that indicate engine temperature. (If your UK version has a coolant temperature gauge in the instrument panel, the same data is used for that.)

Why do you suspect the sensor?

 

Thanks plain om. I suspect the sensor as I'm experiencing intermittent hesitation, stuttering etc, but only when the engine is cold, ie when that little blue light is on. Once that light goes out, car runs like a champ. As it doesn't always do it, and issues never occur after light goes out, I thought it might be a likely culprit. No cel or codes though.

 

Also the idle occasionally goes up and down a few times for 5 seconds or so on a cold start.

 

I doubt the ECT sensor is causing the symptoms described here and in your other thread on this same issue: http://www.subaruoutback.org/forums...rums/66-problems-maintenance/466313-stuttering-throttle-response-when-cold.html

The problem description in the other thread could point to a vacuum leak in the intake system, or a faulty MAF, A/F, or O2 sensor.

A scanner that can display, and better still, record, engine information including sensor signal values and fuel trims, might reveal an anomaly. One of the data series that is available is the ECT, so this could also verify if the sensor and the temperature light(s) are working properly.

Perhaps look into Romraider. It's a free program, specifically for Subarus. It runs on a Windows or Linux system (e.g. portable laptop), and an inexpensive adapter cable to link the computer to the car's OBD connector. I believe it will work with your UK 2011's ECU, but I'm not certain. See RomRaider - Open Source ECU Tools | RomRaider / RomRaider, and do a title search here for thread titles that include Romraider -- there's some that provide more information on setting up and using the program to advantage.

 

Thanks again plain om. The service manual refers to the CTS as a possible cause of my symptoms, especially if they only occur at lower temperatures. It also lists map,maf, crank,cam, throttle control etc but specifically mentions CTS at cold temps.lve hooked up active OBD and the blue light goes out when the coolant temperature reaches about 49 Deg celcius (120 Deg f). Does this seem about right?

 

I don't have any data on when the blue light should go out. @scoobydoo2 has reported coolant temperature versus lights on/off (http://www.subaruoutback.org/forums...010-2014/467561-relationship-between-intake-temperature-engine-temperature.html) and perhaps might also have the temperature at which the blue light normally goes off.

One interpretation of the sensor impact is that problematic engine operation when cold, but not when warmed up, could be caused by the coolant temperature signal being too high when the engine is cold; e.g.,, the engine might be at 20 C, but the sensor is signalling 85 C. As a result, the fueling is calibrated for the engine at normal operating temperature rather than one that's cold.

After the car has been parked for some time, say, overnight, turn the key just to On (not starting the engine) and check the coolant temperature indication on your Active OBD readout. It should be at or close to the ambient temperature where the car is parked. Then, drive the car for some time and see where the temperature seems to stabilize; I would expect it to be roughly in the 85 - 95 C area. If this is the case, then the sensor itself would likely be working properly.

Also, your readout should have Ambient Temperature, and Intake Air Temperature. When the engine is cold, and off, all the temperature readings should be the same. Incorrect Ambient Temperature and/or Intake Air Temperature can also affect engine performance.

 

The blue light goes out when the coolant hits 120 - 122 degrees F....Yup...I've checked on that one with my ultraguage too...:smile2:

 

Thanks again guys. My coolant temperature is as described by plain om, and air temp and intake temp seem ok too. This is frustrating. I think I'm going to have to let it develop until a code is set, hopefully. Maybe check for vacuum leak too.

 

Any ideas what could cause this without setting a code?

 

Some codes are set only after a fault is detected in two consecutive drive cycles, and then only if other criteria are also met. A symptom that shows up only in 1 in 10 cold start-ups, and might not be repeatable within a single drive cycle, might also not meet the requirement to set the CEL. Other codes, such as misfires, will flash the CEL at the time and ultimately set the CEL in a single drive.

I believe your active OBD is part of the Torque or Torque Pro app. That should be able to read OBD engine codes. Sometimes, if a fault is detected in a drive cycle, the ECM will not turn on the CEL at that time (as noted above), but might save a "pending" code for that fault. Some OBD code readers will show "pending" codes. If you haven't already tried it, next time the car is exhibiting the hesitation, check to see if the app shows any pending codes at that time. (If there are any codes, do not use the app to clear any codes that are identified.)

Hesitation etc could be almost anything related to engine operation -- fuel, air, spark.

Incidentally, I've attached a table showing the range of data (parameters) that the ECM can provide to OBD scanners. Your app might be able to readout many of these. The table is based on an engine that's fully warmed up and idling, so the values indicated wouldn't apply to when your symptoms appear, but even then some faults can show up in the data when the engine isn't yet at it's normal operating temperature. So perhaps monitoring the data when the symptoms don't appear could provide a reference for when they do.

Also, I wonder if the LPG flexibility might be a factor. I understand it is prevented from switching to LPG when the engine isn't warmed up, but is that determined by the status of the light, or is it based on the actual coolant temperature? is the switch to LPG automatic, or manual, and if automatic, how do you know when the system switches over?

 

Thanks again for the detailed response. The lpg switchover is automatic and is determined by coolant temperature, about 50 c, at same time as light goes out. The car cannot be started from cold on lpg. The car runs perfectly on petrol or lpg when warm. Once up to temperature, the car can be switched between fuels manually via a switch in the cab. Problems are only present in a cold engine. All temps on the obd app seem ok.

 

One thing I like about the ultraguage is that all the stuff that @plain OM has mentioned is easily accessed and displayed. One thing I have on all the screens is my engine temp...in degrees f even though we use metric. Normal temp in degrees C is 90...194 f. After losing a HG I pay attention to these things...

 

Ok, so spoke to my lpg guy today and mentioned this issue. He raised the issue of the petrol injectors being a bit gummed up, as they don't see a lot of use, only really during engine warm up. He said this can sometimes be an issue with dual fuel cars. He recommended putting some injector cleaner in the tank and running exclusively on petrol for a week to see if the issue resolved. Did this today so we'll see.

 

So, I ran some petrol injector cleaner through, and ran exclusively on petrol for a week. I also added some stuff called archoil 6200 to the next tank, the guy at the parts shop gave me a free sample.The hesitation seems to have gone, and the car seems to be running a little sweeter now, on both petrol and lpg. So cautiously chalking this up as a win!