Avensis warning light on but no fault code found

Avensis 2001 Mileage 115,000 One month ago, warning light comes on. Service is due anyway. Regular garage (not Toyota dealer) does service, identifies faulty oxygen sensor
(there are 3, the faulty 1 is on the left exhaust manifold). Orders replacement sensor. Takes 2 weeks to arrive (remember earlier this year there were major problems with contaminated fuel from Tesco that damaged oxygen sensors on a wide range of cars).
Replacement fitted, warning light cleared.
2 weeks later, after driving about 1000 miles, warning light on again. Garage says their diagnostic kit shows "no fault found". They clear the warning light. 3 times since, I drive anything from 10 to 30 miles, warning light comes on. Garage clears light, again says "no fault found": repeatedly.
I ask at Toyota dealer. They say their diagnostic kit never reports "no fault found". Is this believable? What about an intermittent fault?
Is there any published information about what faults cause the warning light to come on?
Any ideas gratefully received ...
-- Graham
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

The OBD II diagnostic system is supposed to store a trouble code if the check engine light is illuminated, even if it is an intermittent fault. I would have the dealer scan the codes and see what they find.
--

Ray O
(correct punctuation to reply)
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I looked over the shoulder of the mechanic at the local garage when he connected his diagnostic kit. It very cleary showed "no error codes found". I didn't note the make of tester, but it's a hand-held gadget about 4 inches wide by 8 inches long, and perhaps just over an inch thick, with an LCD display of 4 or 5 lines of text at the top. It connects to the car with an adapter cable to suit the car, with a mini-DIN connector (looks like a PC keyboard connector) into the tester itself.
I think this is some general purpose device that has a library of settings for a range of cars. I accept that it is possible that the control computer in the car can store error codes, and that the tester does not know how to interrogate the car for stored error codes. But it does seem rather pointless for a manufacturer to make a tester that does not know how to find out the stored error codes.
Anyway, I have booked it in to the Toyota dealer for next Wednesday morning. There is a charge (45) and they say allow an hour. They admit that there are occasions when the error light will show but no stored error codes are found, in which case debugging the cause of the problem can be really difficult. Presumably we are then looking at the possibility that the control computer itself is faulty?
-- Graham
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I believe that there are instances where the MIL is illuminated but no trouble code is stored.

Yes, it is possible that the control computer itself is faulty, but those instances are very rare. I'd wait to see what thee dealership comes up with.
--

Ray O
(correct punctuation to reply)
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Could this happen during DMV inspection as well?

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

It depends on the DMV inspection process and the type of on-board diagnostic system. I believe that in most states in the U.S., having a check engine light illuminated is an automatic fail, regardless of whether there is a code stored or not. For pre-OBD II vehicles, the emissions test involves probing the exhaust pipe to sample the exhaust gases. For OBD II compliant vehicles, the testing facility hooks a code scanner up to the OBD II test port under the driver's side of the dashboard.
I think the OP's Avensis was a 2000 model, and since the Avensis is not sold in the U.S., I am guessing but am not sure that it is OBD II compliant.
--

Ray O
(correct punctuation to reply)
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
"Ray O" <rokigawaATtristarassociatesDOTcom> wrote in message

It's an Avensis Vermont, 1.8 litre engine, actually bought by the first owner in 2001, but may be 2000 specification.
In the UK we have an annual MOT test (for cars over 3 years old) which checks safety and emissions, but the emissions are tested with an exhaust gas analyser rather than taking any notice of the car's own warning systems.
-- Graham
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
<snipped>

I should clarify a little bit... On some vehicles like the Camry, there is a separate transmission control module (TCM) that stores transmission trouble codes. It is possible for the TCM to detect a problem and illuminate the MIL but an entry-level code scanner might only be able to read the trouble codes in the engine control ECU and not the TCM, so it wouldn't see any trouble codes. Technically you are correct, but some code scanners would not be able to read the codes.
--

Ray O
(correct punctuation to reply)
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Tried another Toyota dealer. They accept that their diagnostic kit might not find an intermittent fault - so I am encouraged.
I book the vehicle in for them to investigate.
Their report says fault code is DTC P1349. This is explained as "VVTi system malfunction (B1)".
They advise checking OCV for cleanliness and replacement of CCTi controller.
They also suggest oil and filter change with flush; this despite the fact that the oil and filter were changed only a month ago (probably 1500 miles)
Can anybody explain this in more detail for me? If the VVTi system is malfunctioning why is the vehicle performing as normal?
-- Graham
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

VVTi is variable valve timing with intelligence. B1 is Bank 1, or the bank that contains cylinder #1.

I'm not sure what OCV and CCTi is. Did you mean PCV (positive crankcase ventilation) and VVTi?
I recall seeing some service bulletings regarding the VVTi controller in some U.S. spec models, there may be bulletins for your car.

I wouldn't bother until it is due for the next oil change.

The performance gain or loss from the VVTi system is not really noticeable by the driver, especially if performance deteriorates over time. If the VVTi system is not working, then you just end up with a car with normal fixed valve timing - up until variable valve timing was invented, all cars had fixed valve timing.
The lack of VVT won't hurt your car, and as you've noticed, probably won't hurt performance that much. The biggest annoyance with a malfunctioning VVTi system is the illuminated check engine light.
--

Ray O
(correct punctuation to reply)
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
"Ray O" <rokigawaATtristarassociatesDOTcom> wrote in message

I'm told OCV = Oil Control Valve. CCTi is a typo, should be VVTi

-- Understood
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.