PO121 code still on, replaced o2 sensors, replaced cracked air tube, put seafoam in gas. reset computer, light came back on after 40 miles. same codes. DIAGNOSTIC TROUBLE CODES PO171 System Too Lean PO171 System Too Lean What next?

Have you had the vehicle scanned for codes?

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Once you have the codes, you can look them up on the web. Just do a search ' 94 Lincoln town car code.....' Just plug in the code(s) number.

P1166 pertains to the upstream O2 sensor heater circuit. P1167 pertains to the upstream O2 sensor output.

code p0420 refers to the cat converter system-bank 1--efficiency below threshold===causes --wiring--cat converter -- HO2S 2. I would replace the heated oxygen sensor number 2. There is no real life on cat converters as they are extremely fragile and run at extreme temperatures which means that if you hit a icy puddle of water / snow and the cat is hot they are prone to cracking and disintergrating internally and blocking up the exhaust pipe.. In your case I would be looking at the sensor. Use the correct tool so that the wires are no damaged.

P0131 - O2 Sensor Circuit Low Voltage Bank 1 Sensor 1 (sensor is before the catalytic converter)

Possible causes- Front Heated Oxygen Sensor Bank 1 harness is open or shorted
- Front Heated Oxygen Sensor Bank 1 circuit poor electrical connection
- Faulty Front Heated Oxygen Sensor Bank 1
- Inappropriate fuel pressure
- Faulty fuel injectors
- Intake air leaks may be faulty
- Exhaust gas leaks
P0132 - O2 Sensor Circuit High Voltage Bank 1 Sensor 1
Possible causes- Front Heated Oxygen Sensor Bank 1 harness is open or shorted
- Front Heated Oxygen Sensor Bank 1 circuit poor electrical connection
- Faulty Front Heated Oxygen Sensor Bank 1
- Inappropriate fuel pressure
- Faulty fuel injectors
- Intake air leaks may be faulty
- Exhaust gas leaks

I am not really sure what is going on here with the same O2 sensor giving these lean and rich codes, if nothing else is apparent and the engine runs well you may have a defective O2 sensor.

crack could cause o2 sensor to read inccorect and light to come on..

What was the exact code? The O2 sensor after the Catalytic Converter, or Rear O2 Sensor, could be faulty which would cause the computer to think the Catalytic Converter is not working efficiently. The code can be reset at the auto parts store with the same code reader they used the first time. P0420 is the most commonly thrown OBDII code pertaining to catalytic converter efficiency below threshold. I would replace the O2 sensor after the Catalytic Converter and reset the computer to see if the code comes back. If it comes back you may have a bad catalytic converter, exhaust leak, damaged exhaust pipes, damaged O2 sensor wiring/connectors, plugged catalytic converter, etc.

I’m happy to help further over the phone at https://www.6ya.com/expert/jeremy_69f3cc28d95bf514

Even though your O2 sensor is showing good by your scan, it could be lazy in giving readings. It has less than a 10 second window to give the reading especially if it is a heated O2 sensor. Try a Bosch unit.

The best thing to do is go to Auto Zone and get your Hyundai scanned for a DTC code. That would tell us which O2 sensor has gone bad. You have three O2 sensors and one of them has gone bad, the O2 sensor sends signals to the ecm to control the air fuel mixture so it will not run to rich or to lean which is causing you to fail the state inspection. Good luck and keep me posted on what the DTC codes are, be glad to help.

unhook the battery for about 15 minutes and hook it back up... that should clear any codes and reset the light. if you have an anti-theft radio make sure you know the code for it and how to enter it.

I have the same problem as talked about above. 2002 Hyundai accent gsi. HORRIBLE gas mileage. I only get about 320 km per full tank. My driving habits are good. i took it to the garage and they put it on the computer and no error codes showed up. Question: Can a MAP sensor be faulty but NOT show up on the computer diagnostic? I had my O2 sensor checked out and my exhaust, and changed the flex pipe. Car runs pretty good just horrible gas mileage and kinda crappy power. Changed fuel and air filter. Cleaned the fuel system entirely ($80 at garage not $4 bottle).

Anyone ever use a resistor in the MAP sensor?