Knowledge Base

Diagnosing a faulty oxy sensor causing high emisions and MOT failure

Checking your OS sensor
by Andy Keeble

There's two easy ways to check your sensor, from the 3S-GE book for Oct 93 engines and later (also works on later turbos);

Warm up the engine and attach an analogue voltmeter between +ve to term VF1, -ve to term E1. (on about the 15v scale)
Run engine at 2500 rpm for 90secs
Short out using SST (bit of wire) terminals TE1 and E1, maintain engine speed at 2500rpm, check the number of times the voltmeter needle fluctuates in 10 seconds, should be 8 times or more. (mine gave about 0.5v out and didn't fluctuate!) If < 8 times the sensor is broken, also the sensor heater when at 20 degrees C is between 5.1 and 6.3 ohms. It's the two wires that are the same colour, (white or black I think). To test this you will need to get the car up on ramps and unplug the sensor, it's in a bitch of a position on a NA, right where the exhaust passes over the rear suspension cross member. The plug for it clips up under the engine. A new sensor from Toyota is about '130 + VAT but I got a universal equivalent for '50.including the correct adapter plate. Now my engine does exactly what it says in the book, revs better etc,

If the sensor is broken or the engine is running out of tune etc, do yourself a favour and get more power/economy etc and sort it. After fixing my emissions were 0.28% CO, running ordinary unleaded

Faulty oxy sensor
by Andy Keeble

My car had failed the MOT on emissions (8% CO). I had diagnosed a faulty oxy/lambda sensor which, interestingly enough, brought up no ECU error codes but when removed was obviously broken (it is ceramic). It must have been outputting a value that was not being seen as a fault by the ECU, and the heater circuit was intact, but no voltage pulses on the VF term on the test connector. I set about finding a replacement; Toyota wanted '130 + VAT and a breaker waned '50 for a second-hand one, and even then it wasn't the original part no etc. However I found a place on the net (http://hglmotors.co.uk) that seemed to know a lot about ECU stuff etc, and the guy there, Graham, sorted me out a Webcon universal sensor and a plate made for Toyotas, all new, plus data sheets etc for '52. After fitting it the ECU was now getting the prescribed >10pulses/10sec VF voltage pulses. Now it drives like a new car, not surprisingly more low-down smoothness and hopefully better mpg. I took if for an MOT and it passed ok with CO now 0.24%! So if anyone has emission problems check that oxy sensor using the test procedure in the 3sge engine book, even if the ECU is clear of codes. You can buy your new sensors from hglmotors.co.uk, they are most helpful, the same sensor mine uses is the same as the 94 turbo and many more I guess. I'm really pleased that I fixed it and learned a lot about my cars whole EFI system, those service books are excellent.