T22 3SFE, sporadic "Check engine" warning light (error codes 12 + 42)

[farbro]

The "check engine" warning light on my 1999 Avensis T22 3SFE Automatic has started to go on and off. After a cold start, it usually takes a few minutes before the light goes on, and it continues to go on and off at irregular intervals, as it had a bad connection or something. The engine appears to run normally.

I recently replaced the timing belt on my own, and I have since been driving 1500 km before the warning light started showing.

I managed to extract some error codes by shorting pin 3 + 14 in the ODB connector. The error codes are:

Engine:

12 = Crankshaft Position Sensor (P0335)
42 = Vehicle speed sensor (P0500)

Transmission: (O/D light):
42 = Speed sensor (or output speed sensor) (P0500)

Source: https://www.auto-manual.com/fault-codes/error-codes-toyota/

I suspected a bad connector to the cranshaft position sensor (since I recently did some work in that area) and started troubleshooting the sensor. The resistance is 1.5 kOhm, and the signal looks like this in an oscilloscope:

I can exclude bad connection since the signal did not change when fiddling around with the cable.

Any ideas on how to proceed with the troubleshooting?

[flash22]

Is it coil on plug or does it use a distributor ?

12 and 42 can be related if the engine speed doesn't the road speed, does the gearbox work as it should ? Any  jerkiness ?

 

 

[farbro]

12 hours ago, flash22 said:

Is it coil on plug or does it use a distributor ?

Is wasted spark an option? I can't find a distributor, but I find two coils.

Quote

12 and 42 can be related if the engine speed doesn't the road speed, does the gearbox work as it should ? Any  jerkiness ?

Interesting! The gearbox also works well, I haven't noticed any issues with the car. So the ECU estimates the road speed and matches it with the measured speed? Where is the vehicle speed sensor located?

EDIT: I should also add that the speedometer works as expected, I assume that would not be possible if the vehicle speed sensor is bad?

[flash22]

VSS is generated from the ABS system (if fitted) and/or the gearbox

The 42 may be a red herring

42 Vehicle Speed Sensor (VSS)
No speed sensor signal to ECU when loaded driving condition with engine speeds 2000 to 5000 rpm.
For 8 seconds or more. (rpm is generated from the crank sensor or an ecu calculated value)

Looking at code criteria - code 12 - crank sensor - Lost of signal >2 seconds

It could well be a sensor breaking down under load - like any intermittent fault they can be a pain to trace

[farbro]

Thank you. Where did you get those  error code specs from?

I realized that the warning light even turns on while standing still and idling. I did a reset of the error codes, turned on the engine and waited for the warning light turn on, and then checked the error code. This time, only code 12 was reported.  So we can ignore code 42.

I am now searching for data sheets for the crankshaft sensor to see if my measured values are within specs.

[flash22]

i did look up the spec's as i was going through the info 1.4 - 1.6k is within range, but that could change due to heat and various other factors

TBH pulling the sensor and cleaning the gear may sort it

[farbro]

My newest discovery is that the light only turns on at low rpm's, < 1100, and it turns off as soon as I go above the threshold. My theory is now that it simply doesn't induce enough voltage at low rpm's. I measured the wires between the sensor and ECU for voltage drop, but they seem ok.

I will take it apart and check for debris or misalignment. I also ordered a new sensor, just in case.

[farbro]

I took it apart and found a tiny bit of metal powder stuck to the magnetic sensor and brushed it off, but but it didn't help. Misalignment is impossible since there is a guide pin holding it in the right position.

After lots of trouble (tip: don't trust i Autodoc.com's catalog) and waiting I received the new sensor and installed it, but the problem persists. Any ideas? I already checked the wiring, but thinking about doing it again due to lack of ideas.

[flash22]

Scope your cam shaft sensor as they share the same ground

[farbro]

Solved! The camshaft sensor was a bit loose and had come out, I just pushed in back in and the warning light turned off. It's probably my fault from the timing belt replacement. So many hours and money wasted on such a simple problem. I blame the misguiding error codes.

Thank you @flash22 for all help!