Toyota Avensis - Malfunction light, contact Toyota dealer. Code PO793/P0793 (later P0717)

Recently, immediately after starting my Toyota Avensis I noticed an orange light appear on the dashboard. I headed straight home as I didn't know what the warning light meant and thus whether or not the car may stop.

Upon arriving home I checked the service book and the light was listed as a Malfunction indicator lamp. The action to be taken was "Take vehicle to Toyota dealer".

I haven't used a Toyota dealer for servicing my car for quite a few years so I contacted my motor mechanic. He suggested I bring it in. He did a test and the test returned a code of PO793 (or P0793) which indicated a speed sensor issue.

What was weird is the issue was intermittent and took some time to track down. In the end my motor mechanic swapped the two speed sensors around and the problem was resolved. It is quite possible that sensor is on its way out and will eventually fail, but swapping the two sensors fixed the issue for the moment (about a month).

The symptom that indicated there was a problem is when I drove the car home, a distance of around 20km, the only thing I noticed, and it only occurred once, is the automatic gear change seemed to be sluggish and lacking power. Other than that I had no problem.

When the motor mechanic had the car he reset the malfunction warning light and took the car for a test drive. The car again had an issue changing gears. However his test equipment indicated the speed sensor was not faulty. Further testing by an auto electrician was on the cards but before that swapping the speed sensors was tried and the problem was resolved, at least for the moment.

My next step is to find out what the signs are for the second speed sensor if it malfunctions. At least I know the speed sensor is a future potential problem.

I hope this helps others who find themselves in the same situation. I couldn't find any others having this particular issue when searching the internet so hopefully someone finds this post useful. At least you know you can swap the speed sensors.

I don't know if taking the car to Toyota would have been cheaper as they may have suitable spare parts they could swap in to test. The total cost of repair in this case was $260. I suspect this was largely the time involved due to the problem being intermittent.

For the future and for my own reference, the following are the symptoms I'll be watching for.

Cruise control does not work

Malfunction light comes on

Delayed shifts

Hard shifts

Limited gear operation

Erratic speedometer

No speedometer reading

Keep in mind I have no real skill with cars so rely on others to fix car issues for me.

Kelvin

Update: 8 Aug 2021

The malfunction light came on again recently, so I combined a visit to the mechanic with a timely service. I was interested in finding out the test code as the two speed sensors had been swapped. This time the code was P0717, a different code, which to me confirms that particular speed sensor was the problem and no need yet to be concerned about the second speed sensor. I was told speed sensors cost around $180 so replacing both when nothing might be wrong with the second speed sensor to me wouldn't be warranted.

Update: 19 Feb 2022
The malfunction light had been coming on and offer over the past few weeks. This time I decided to take the car to a Toyota dealer as they would have better access to spares. The error code was P0717/37 which again was a speed sensor code. However, as explained to me with further investigation the ECU was found to be faulty and was replaced with a second-hand ECU as a new ECU was if I recall correctly going to cost around $2,300 for a new unit alone.

The cost to replace the ECU was $1,136.00

Update: 24 Feb 2022
The second day after having the ECU replaced the malfunction light again came on. I took it back to the Toyota dealer but unfortunately the light didn't come on for them and no error code was present. I collected the car and again the next day the light came on so I returned to the Toyota dealer with the engine running and the malfunction light on. After some investigation the issue and error code appeared to indicate the O2 sensor was faulty.

When I returned to pick up the car today the issue wasn't the O2 sensor but a sensor with an error code of P0737. The  sensor was replaced and the malfunction light is currently off. I'll see what happens next.

The cost to replace the transmission speed sensor was $144.80. No labour was charged.

Update: 13 July 2022

I'm not a motor mechanic and can't tell one sensor from another. I just have an uncomfortable feeling there was no need to replace the ECU since the problem wasn't fixed after the ECU was replaced. There's always the chance there were two problems with one masking the other. Since I don't know enough it's just best to move on. My car's now working and that's what's importnat.