Code PO138

P0138 - Oxygen Sensor Circuit High Voltage (Bank 1 Sensor 2)

Fault codes never say to replace parts. They only indicate the circuit or system that needs further diagnosis. The only way to set this code is to have a break in the sensor's ground wire or the signal voltage wire is shorted to the 12 volt heater wire for that sensor. Start by looking for a corroded terminal in the sensor's connector or a terminal that got stretched or pushed out of the plug body. Next, check the wiring harness for signs of melted wires, especially where they travel near hot exhaust parts.

If you haven't found the cause by this time, use a scanner to view live data and look at the sensor's voltage compared to the passenger side sensor. If it's normal, you have an intermittent problem that isn't currently acting up. Try flexing on the wire harness to see if the voltage changes. If the voltage IS high, unplug connectors going to that sensor and wiggle harnesses until the voltage changes. That will help you narrow down the location of the problem.

Nope. We're looking for a problem in bank 1. The next thing is to use a scanner to see what the Engine Computer is seeing so you can figure out why it is setting that code. It would be very rare to have a shorted sensor, and really rare to have a new one also shorted and setting the same code, but if the wires will reach, you can switch the plugs between the left and right sensors, then erase the code and see if the same one comes back. If the sensor has a problem it will set a new code for bank 2. Switching the rear sensors won't affect how the engine runs.

I have answers for all your questions but the web site keeps reloading over and over and it's erasing what I type. I'll try later.

The ticking can be caused by an exhaust leak. If it is ahead of the catalytic converter, in between the puffs of exhaust gas flow the momentum will create little puffs of vacuum. That can draw in outside air and the oxygen will be detected as a lean condition. The Engine Computer will respond by adding more fuel but there will still be that extra oxygen there.

I've repaired thousands of radios for new and used car dealers in my state but the only bad amp I ever ran into was two years ago in my '93 Dynasty with 4,200 miles. Switch the two rear speakers side-to-side. If the same speaker is dead, look for a small black plastic box bolted to it. There's a capacitor in there that is likely open. You'll have to chisel it out of the protective glop to replace it, or you can bypass it with a jumper wire.

The mirror problem is unusual. I would start by looking at the wires between the door hinges to see if any are frayed and touching.

There's a couple dozen potential fault codes related to the oxygen sensors and each one gets pretty specific. Some simply report the condition, like "running lean too long". Those codes prove the sensor is working; it's just reporting what it sees. Other codes, like 138, report a defective condition in the circuitry. Those tell the computer it can't believe whatever readings it might get. In those cases there is always a backup strategy that lets the computer make fuel metering and ignition timing decisions based on other factors. Those decisions won't be accurate or provide the lowest emissions and best fuel mileage but they will keep the engine running.