Yaris 1.0 2003 decreasing fuel economy

[Bornless one]

My 2003 1.0 Yaris (facelift), when driven at highway speed (130 km/h) has been giving me 6.5-7 l/100 km for the better part of the year (17000+ km). During the last 200 km of my last trip, fuel consumption spiked to 8.5 l/100 km when driven at the same speed. Basically nothing else changed on the car, I've had the same tires (inflated to same pressure), the road is the same one I've driven before, and I've been pouring same gasoline at the same petrol stations.

I've already checked the tire pressure and it is ok, I've pulled the spark plugs, and they are in good condition, I've checked the air filter (which was replaced about 5000 km ago) and it is fine, check engine light is off, I've attached my OBD II reader and there are no fault codes, I have checked the oxygen sensor and it's output is fine. I don't notice any pulling to the side, or other symptoms of a sticking brake pad, and my fuel economy at lower speed (80 km/h) is roughly the same as it was before.

Do you guys have any insight on the matter?

[Madasafish]

Winter

Brakes grabbing.(hand brake?)

Tracking.

Exhaust blocked

Faulty engine temperature sensor meaning rich fuel mixture..

[bathtub tom]

OP doesn't say what country they're in, only that their fuel consumption has been consistent "for the better part of the year".

I'd suggest that with the onset of cooler temperatures, the car's running richer for longer resulting in higher consumption (mine certainly is).

 

[Bornless one]

Hi guys, thanks for your thoughts. I don't think winter is the problem, it has been 15ish degrees in the last 2 weeks, and I have gotten consistent fuel economy during previous trips where the temperature went into the single digits. As far as tracking is concerned, I've went for a wheel allignment about 2000 km ago, and I do not notice any changes in handling so I do not think it is that either.

Correct me if I am wrong, but a blocked exhaust would cause some difference in engine sound? The car idles and runs as it did, I didn't hear anything out of the ordinary.

As far as the brakes grabbing, I will jack the car up, check each wheel and let you know, even though I didn't notice any difference in handling.

Michael, you mentioned the engine temperature sensor, the only ones that I saw via my OBD reader are the inlet air temperature and the coolant temperature sensors, and they both operate normally. Is there a different sensor used for adjusting mixture, and if so, do you know where it is located and how to test it?

[bathtub tom]

3 hours ago, Bornless one said:

As far as the brakes grabbing, I will jack the car up, check each wheel and let you know, even though I didn't notice any difference in handling.

No need to jack it up, just feel each wheel and tyre for temperature after a run. The fronts will probably be slightly warmer than the rears as, I assume, it's not a hybrid.