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Ron Z.
Ron Z., - Toyota Tech -
Category: Toyota
Satisfied Customers: 18966
Experience:  18+yrs experience. State Inspector and Toyota Diagnostics
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Toyota RAV4: check engine light, VSC and 4wd lights are on

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The VSC, 4wd, and engine light came on after we put in gas. We have tried a new gas cap. After taking off the positive side of battery off but after about three times of shutting off and restarting engine the lights come on again. What is wrong?

When the Check Engine light comes on, the VCS and 4wd lights are also set. This is a self-preservation mechanism, that turns these systems off, in case the reason the engine light is on can harm or effect these systems. SO - fix the reason the Engine Light is on, and the other systems will come back online.
When the Check Engine light comes on, this is the on-board computer's way of telling you it sees a problem in one of the monitored systems. Unfortunately, there are literally 100's of parts and sensors monitored in various systems, and to take a "guess" as to which part/sensor in which system is faulty, is virtually impossible. However, if you are not experiencing any drivability issues such as skipping, stalling, shifting problems, etc, then more than likely, the problem is going to lie in the EVAP (emissions control/recovery) system. Very commonly, this could be a faulty, loose or missing fuel cap or even putting fuel in while the vehicle is running can set the light. Check the underside of the fuel cap for any cracks or signs of defects that may keep the cap from sealing correctly. If there are any doubts about the inspection of the cap, replace it. Keep in mind, you will need a cap that meets OE Specs. Those "universal" or "locking" fuel caps sold at after market parts stores do not meet OE specs, and will not seal the system correctly. Check the top of the fuel filler neck for any signs of damage or debris. Check under the vehicle, around the rear areas of the vehicle, looking for any vacuum lines that have dry-rot cracks, holes or loose/missing connections. If these all check out, then the best thing to do at this point is to have the Diagnostic Trouble Codes (aka "p-codes") read from the on-board computer. These p-codes are what is used as a "starting point" for the diagnosis and will tell which part/sensor, in which system, has the fault. There isn't a Mechanic on the planet that can tell you what is wrong with the vehicle just by "looking" at the Engine Light. Every single Mechanic's first course of action WILL be to obtain the p-codes. It's standard diagnostic procedure. Once you get these p-codes you can more accurately and efficiently diagnose the problem and then make the correct repair. You can have these p-codes read FREE (except in California) at any local "big chain" part store (ie. AutoZone, PepBoys, Advanced, etc). If you still need help after retrieving the codes, you can bring them here to me, and I am certain I can help you resolve the problem.

Ron Z. and 3 other Toyota Specialists are ready to help you
Customer: replied 4 years ago.

Our trouble code was p0158. Do you know what that is?

THe P0158 is a very straight forward, and very common fail item on these vehicles. It's pointing to a fault in the Oxygen Sensor for Bank 2 Sensor 2. Inspect the electrical connector and as far up the wire harness as you can looking for any loose, broken or damaged wires. If the visual inspection checks ok, replacing the sensor will solve the problem.

Customer: replied 4 years ago.

We changed the bank 2 sensor 2 and still the lights have not gone out. What is our next thing to try?

Ok. Make sure you replaced the correct sensor (on the side of the engine, closest to the front of the vehicle, below the converter). Next, make sure it was the correct part. If this was a low-quality, or "universal" (you had to splice the wires) it's the wrong one. The Toyota OE part number is: 894650R020 - most local parts stores can "cross over" or "interchange" this part number to the correct version of the after market brand they carry. Make sure to check the fuses in the dash fuse box and the under hood fuse block (labeled in red in images below). Double check the electrical connector and wire harness for any loose, broken or damaged wires. Like I say, this is an extremely straight forward code, and the problem lies in this sensor somewhere. Toyota diagnostics are the tightest on the market today, and if this code is set, there is a problem with this sensor. Not too many other variations.
Dash fuses:
Under hood fuses:

Customer: replied 4 years ago.

Should the lights go out automatically when the problem is solved? Do I need to do anything else to get the lights to go out?

The light will go out after 75-100 miles of normal driving OR you can remove the "NEG" cable from the battery for 15 minutes.