Rav4 Check Engine Light but no DTC

[RNeil]

I have a 1998 Toyota Rav 4 with 110,000 miles on it. I have had a lot of trouble with the check engine light coming on, but there is no diagnostic trouble code. The light would come on for a few days and then be off for a few weeks. Then I got a P0171, fuel trim system lean. The fuel economy also got worse. The idle was sometimes slow. I did some research found that the code is usually caused by a dirty or bad mass air flow (MAF) sensor. I was all set to clean the MAF but I found it didn't have one. Then I got a P0136, heated O2 sensor circuit malfunction bank 1, sensor 2. I cleaned the throttle body, replaced the spark plugs, O2 sensor and air filter. Now it is back to the check engine light coming on with no DTC.



Does anyone have any suggestions? What can cause the check engine light to come on without a DTC?

[deekay140]

if the problem fixes itself, the code will clear after 40 key cycles


replace the other o2 sensor for the po171 code b1 s1

[RNeil]

It is my understanding that only the upstream O2 sensor affects operation. This is the one I replaced. If there was a problem with the other one, I should get a DTC, but the MIL comes on with no DTC.

[BadChicken]

if your getting a P0171 code you need to replace the MAF sensor, cleaning it won't do anything. The P0136 code may be getting set due to all the extra fuel being dumped in. I would replace the MAF and see what happens.

[ShawnM]

I cant remember if the rav 4 has a MAF sensor or a MAP sensor. Either way, if the check engine light comes on there has to be a code stored, unless you have some strange computer problem. The only function the downstream O2 sensor has is to monitor the catalytic converter efficiency. That could turn the check engine light on, but it wouldnt cause the car to run any differently. Unless the converter is plugged up. What scanner are you using?

[RNeil]

I am using the AutoTap scanner. It plugs into the USB port of my laptop.

[shimpi]

You know, if the sensor is alright, I just go under the hood and pull the fuse out for about a minute to reset it. After I stick the fuse back in, the check engine light is off.

[RNeil]

You are right, disconnecting power or using the scan tool to "clear DTCs" causes the check engine light to go out. It also causes the readyness monitors to go to incomplete. And the light comes on again in a day or two. I have now gone about two months without resetting it. All the monitors are complete except for the catalyst.

I was fortunate that in August the light went out long enough for it to pass inspection. But it will not pass with the MIL on. I can reset it, but then it would fail because of too many monitors incomplete.

[palominas2000]

I also have a similar problem, I own a 2004 RAV4, the MAINT REQ light flickered on and off for a few days and yesterday it stayed on. My son did a computer test and no codes were shown. Now I need to know how to turn off the light. I am not too savy about cars but have plenty of help from my son. thanks