P0116 - loss of power and stalling

I went out with the family to Johnson Valley to watch the desert race at KOH this weekend. We started to have some issues with the car losing power while driving over whoops or harsh terrain. It also stalled on me probably 6 times while getting it back to pavement. It never threw any codes and back on pavement no issues. We went back out today to watch a little more and try to diagnose more. It finally threw a code. P0116 - temp coolant sensor. I cleared it and the problem persisted. It never ran hot. Only did about 15 miles in the dirt today but never pushed it to avoid it stalling. Drove it home to San Diego and mostly fine but a couple of times going over rough highway I could feel it cutting power a little.

2 questions:

1) where is the temp coolant sensor on these vehicles? 2018. Any advice on replacing?
2) why is the car stalling?

 

The ECU would likely use a signal from coolant temp to know if the engine is at normal operating temperature for a proper fuel to air ratio in the cylinder. I'm thinking that if the coolant temperature was to go away then the ECU would process as the engine cold and go to a too rich mixture.

 

^ and in order to protect the engine then the ECU just decides to cut power or shutdown completely the engine. Odd though that this is happening. Check the coolant lines and make sure you don't have cracks, leaks. Also inspect the quality of the coolant and observe for overheating events. Good luck.

 

Just thinking about the way this problem manifests itself, when you find the location of the coolant sensor on the engine, check for a loose connection.

 

Got this from the enterwebz AI Monsters:



P0116 –

Engine Coolant Temperature Circuit Range / Performance

On your 2018 4Runner (1GR-FE) this means the ECU thinks the coolant temp reading doesn’t make sense over time (too slow to warm up, jumps around, or disagrees with reality).


This is not usually a dead sensor — it’s often thermostat or wiring related.

Most common causes (in order I see them on 5th gens)

1️⃣

Failing / stuck-open thermostat

⭐

most common

• Engine warms too slowly
• Heat may be weak at first
• Code often sets after highway driving
• Gauge may still look “normal” (it’s heavily damped)

➡️ Fix: Replace thermostat (OEM Toyota highly recommended)

2️⃣

ECT sensor drifting

(even if it’s not “bad”)

• Sensor reads, but values are inconsistent
• ECU sees temp not rising smoothly → throws P0116

➡️ Test: Compare live data to reality (see below)

3️⃣

Low coolant / air pocket

• Especially if coolant was recently serviced
• Air passing the sensor causes erratic readings

➡️ Check: Radiator level (engine cold), not just overflow

4️⃣

Wiring / connector issue

(less common)

• Heat + oil contamination near the connector
• Corrosion or stretched wires under the intake

Quick tests before replacing parts


Scan tool live data test (best)

• Cold start after sitting overnight
• ECT should read within ~5°F of ambient
• Temp should rise smoothly to ~185–195°F
• If it creeps forever → thermostat
• If it jumps or drops suddenly → sensor or wiring

Physical check (old-school but useful)

• Start cold, feel upper radiator hose:
  • Should stay cool for several minutes
  • Then suddenly get hot when thermostat opens
• If it warms gradually from the start → thermostat stuck open

If you’re replacing parts

Thermostat

• Use Toyota OEM (aftermarket ones cause repeat P0116)
• Replace gasket
• Bleed coolant thoroughly

ECT Sensor (if needed)

• Two-wire sensor under intake (as described earlier)
• Use OEM or Denso only

Pro tip

If you replace the thermostat, you fix P0116 about 80–90% of the time on these trucks. Many people change the sensor first and the code comes back.

 

Dang That AI is getting good....

 

Thanks for the thoughts. I found the manual on the other . Looks like I need to remove the intake manifold to get to the sensor. So I guess I'm going to try the thermostat first (after checking the wires). We tried checking the wires out in the desert, but we had no idea where the sensor was located. I feel like it's going to be wire/sensor related due to the conditions required to make it misfire/lose power, but the thermostat will be way easier to replace.



Here is the information needed to remove the intake manifold:

 

Any chance this is a loose battery cable, corroded ground strap, or damaged battery? I only mention it because it seems odd that the loss of power is so directly related to going over bumps or whoops. You’d think that if it’s going into limp mode due to a bad sensor reading, that the ECU would command limp mode in an “all or none” fashion and stay in limp mode as long as it’s running.

It’s possible it’s damaged wiring like you suspect. Maybe some little desert creature got in there and nibbled on some wires? It might be worth getting a cheap little bluetooth borescope camera to look around under the manifold before committing to taking everything apart.

➡️maybe I should start jazzing up my posts with arrows, dots, and whatnot❓⭐️⭐️⭐️
⬆️

(WWAID?)

 

I poked around last night. I don't think I need to remove the intake manifold to get the sensor out. The wires appeared to be fine. I meant to check the battery ground last night but I forgot.

I agree with you McSpaz. I don't understand why it's happening during whoops. It doesn't make sense to me.

 

The enterwebz AI Monsters reply to my question decided to spiff up my answer with all those extras, but I see you found some on your own to put in your post.

Are you one of the AI Monsters @McSpazatron?

 

Well, I guess the little do-dads are harmless. Just be glad you didn’t get the mecha-hitler version of AI when you asked your question. That would have been awkward lol.

 

The good:
I replaced the sensor. It was $100 at Toyota. Pretty easy. Need a deep socket 19 mm. I had a 12 point that wasn’t deep enough but my 6 point was. Just the internal cavity wasn’t big enough to accommodate the wire connector.

About 1 quart of coolant came out. I’ll need to pick up some more tomorrow.

The bad:
I noticed a little piece of black plastic from the connector broken off while installing the new one (the hardest part was keeping the washer on while getting the sensor into place). I don’t know if that’s why the old one was having issues or if I made a different problem. The connector did not pop off the old sensor easily, so I’m leaning towards a new different problem. Replacing that connector will not be easy…

 

thanks for the update, I’m making a mental note and screenshots for knowledge.
@coryanderson did you address the thermostat or anything other point Saker noted, which recommended holding off on sensor replacement as the first step? Also I’ve definitely had weird things happen when battery or fuse connections were loose

 

I did not replace the thermostat. The car is warming up correctly and it’s not overheating. Also, because of the conditions required to generate the loss of power, I don’t think it’s a mechanical device failing.

For the record: I don’t think replacing the sensor is going to solve the problem either. It was simply the easiest thing to do first. <— I did check wires, looking for rodent damage anywhere (my dually has had something similar and that cost $1,200 in labor to replace wire behind the fan, so this was a real possibility, still is), check the grounds, and I doubt it’s coolant related, once again due to the conditions required to make it lose power/stall.

I also started to think back a while and I believe this issue has been around for a bit, I’ve been trying to recreate it while driving my daily drive and realized it’s happened before, I just chalked it up to that stupid Atrac kicking in.

 

copy that, interesting, I do not envy you! that sucks. if you’ve had vehicle rodent damage on the same property before, that certainly could be plaguing you