Tata Tiago AMT: Facing engine temperature sensor issue regularly

With this, the car goes into a 'limp' mode. The creep function stops working. Gearbox refuses to up-shift beyond 2500 RPM and 2nd gear.

BHPian Dr.Suraj recently shared this with other enthusiasts.

I have been an 'overall' happy Tata Tiago owner for 4 years, ten months, and for 30,000 km as of date. The first batch of the AMT Tiago - I have an XZA Petrol with a 1.2 NA 3 cylinder Revotron engine and the 5 speed AMT 'head nod' auto box.

But, where there's Tata - the happiness is often short-lived. As robust as the build quality is, and I must confess, this one has behaved LEAST like a Tata for all of 4 years. No niggles. No rattles. No recurrent gremlins. The doors closed with a thud; the steering always felt nice and weighed up well. The ride was soft, and the overall car felt solid(further testimony lies in the hits it took and stood strong to tell the tale).

Not sure what was the weaker point - the engine (3 cylinders) or the AMT gearbox. I, for one, could never tolerate the car in City mode and my defacto mode was sports mode.

Now, to the problem: On a lovely Sunday morning in September 2021, after a 20 km spirited highway drive - suddenly - out of nowhere - the engine temperature gauge (digital) goes to ZERO. No, not one bar. NO BARS. Blank. Gone. And, the engine coolant temperature sign comes on. (red colour). This is different from the CEL and the Engine Temperature high sign (as per the manual).

With this, the car goes into a 'limp' mode. The creep function stops working. Gearbox refuses to up-shift beyond 2500 RPM and 2nd gear. Switching between Auto and Manual mode makes it change gears to a notch higher.

Even though it was a Sunday, Tata Support responded well - via the helpline - and the senior manager from the workshop was with me on call to try and figure out the problem.
After some basic tests - coolant check, engine oil leakage, etc., he assured me it is safe to 'cautiously' drive it home. So I did precisely that, intending to go to the workshop the very next day.

The next day, I start the car - everything is NORMAL! As if nothing ever happened. As if it was a bad dream. Still, we took it to the workshop. Scan shows up the error codes. Those are cleared.

Since then, every month - month on month - this problem RANDOMLY keeps coming up under all kinds of varied circumstances. Sometimes cold start, sometimes in the middle of a drive after 15 to 20 km. Sometimes after revving hard, sometimes for no apparent reason!

As erratic and mysterious as the appearance, equally mysteriously, it just disappears. Sometimes it lasts for 2 seconds, 10, 3 minutes, sometimes it remains for hours or even overnight.

Multiple visits (with equally hilarious Murphy's law type of outcomes) to the Tata workshop led to the following changes (step by step):

• Oil filter change.
• Engine coolant temperature sensor change.
• Coolant thermostat sensor change.
• Oil temperature sensor change.
• Radiator fan change.
• Fuel tank cleaning.
• Fuel line cleaning.
• Spark Plug cleaning and refitting (sometimes it would take a LONG crank, and twice it was checked - battery wasn't the culprit).

Finally, one SA suggested that we change the AMT gearbox. It is a clutch issue. That's when I had panic bells set in. 27k on the odo, 4 & 1/2 years of predominantly city running ... AMT gearbox failure?

A simple email to TML brought the cavalry to ensure a better diagnosis. They did their bit to my car for one whole week. Never told me what they did - but the problem disappeared! I didn't even see it happen for a full two months, and the car felt better than new. The engine was sprightly, the gear shifts smoother, and revved better in Sport mode.

Alas! One fateful day, after the first food court towards Pune, the sign came on for precisely 2 seconds while on the ghats. 2 seconds - and it was gone. The entire trip to Pune, the city, and a few days later, we were back - nary an issue. Next week, in the city - and the problem is back. This time it refuses to go! Car is sent to the workshop when they check the car - the problem is gone! This time, I asked the TML guys seriously - what needs to be done - the answer is:

ECU change and ECU wiring change!

I didn't go ahead with it. But, fortunately, it has been more than a month since then, and the problem has not returned!

But, I know this could happen at the back of my mind. Frankly, the solution scares me. Hence, I seek an opinion based on the experiences of members here ... WHAT IS THIS ISSUE?

P.S:  The reason not to mention any names of the workshop, the SA, or the helpful folks at TML is that as inept as it may seem, I believe that they have given their best and put in total effort. They have been cooperative, supportive, very responsive, and provided whatever best they could to help me solve this problem. Yes, there may be people who say that 'this shouldn't happen in the first place' - or 'that's why you never buy a Tata.' Sorry, but I have seen and heard equally bizarre stuff in ze Germans, and I have already booked a Dark Edition Nexon EV.

Here are MANY videos of this issue. These are unlisted on YouTube. Attempted at capturing that this problem has decided to surprise/embarrass/torture me numerous times.

P.P.S:No mods or tinkering was done to the car. 95% times single fuel COCO HP Pump. Every 3rd cycle is Power. All service and maintenance are done on time at TASS. No other issues to date. The only change is Tigor projector headlamps swapped 2-3 years ago - again TASS with warranty and original components.

Video #7 and #8 show the randomness of the issue.

Any guidance is appreciated.

Thank you in advance.

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