Oxygen sensor

geno_mr2sc · 07-15-2009, 05:47 PM

Symptoms:

ECU Code 21. Cannot clear it. Runs OK but could be better.

O2 circuit voltage seems quite low: .1 - .2v at the Af hole in the diagnostic connector.

Same low voltage exists on both sensor wires that are not heater wires when car is on. OX port on ECU sees .9v - 1v.

I have a parts car, so swapping parts is pretty easy. I have tried a different Oxygen Sensor and a different ECU.

Wiring is a possibility, but it would be the first time wires went bad on this car.

Jackstand Queen · 07-15-2009, 08:41 PM

Don't forget the strong possibility of corroded terminals at the connectors.

Also, the insulation on the sensor wiring that is near the 02 sensor could be brittle, and cracked due to heat.

I think you are on the right track.

Good Luck.

mr2magic · 07-16-2009, 04:46 AM

Check the resistance between all parts of the wiring O2 - O2 and O2 - ECU. You prolly have a wiring problem.

geno_mr2sc · 07-16-2009, 11:09 PM

I am interested in the voltage output on a normal (code-free) MR2SC at the OX port on the ECU. Mine seems low, but the BGB does not show a value for this port.

My understanding of the o2 circuit is that the ECU supplies a voltage (unknown value) and looks for average .5 volts from the sensor on line Af in a pattern that switches from high to low.

My sensor is outputting values in the .1 volt range, but tests OK on the bench (easily puts out 1V, drops quickly, etc.).

At this time it seems reasonable to assume that the voltage being supplied by the ECU from port Ox is not right, but I don't have a normal value to compare to.

dirocyn · 07-27-2009, 04:57 PM

Should be a value between .2 and .7. ECU supplies .45. Here's an explanation of how it works, from people who know a lot more than I do. Oxygen Sensor Information

07-15-2009, 05:47 PM	#1 (permalink)
geno_mr2sc No Skills Join Date: Jul 2009 Location: Flyover Zone Posts: 2 Thanks: 0 Thanked 0 Times in 0 Posts iTrader Rating: (0/0% )	Oxygen sensor Symptoms: ECU Code 21. Cannot clear it. Runs OK but could be better. O2 circuit voltage seems quite low: .1 - .2v at the Af hole in the diagnostic connector. Same low voltage exists on both sensor wires that are not heater wires when car is on. OX port on ECU sees .9v - 1v. I have a parts car, so swapping parts is pretty easy. I have tried a different Oxygen Sensor and a different ECU. Wiring is a possibility, but it would be the first time wires went bad on this car.

07-16-2009, 11:09 PM	#4 (permalink)
geno_mr2sc No Skills Join Date: Jul 2009 Location: Flyover Zone Posts: 2 Thanks: 0 Thanked 0 Times in 0 Posts iTrader Rating: (0/0% )	voltage at OX I am interested in the voltage output on a normal (code-free) MR2SC at the OX port on the ECU. Mine seems low, but the BGB does not show a value for this port. My understanding of the o2 circuit is that the ECU supplies a voltage (unknown value) and looks for average .5 volts from the sensor on line Af in a pattern that switches from high to low. My sensor is outputting values in the .1 volt range, but tests OK on the bench (easily puts out 1V, drops quickly, etc.). At this time it seems reasonable to assume that the voltage being supplied by the ECU from port Ox is not right, but I don't have a normal value to compare to.

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07-15-2009, 08:41 PM	#2 (permalink)
Jackstand Queen Cage Fighter Join Date: May 2008 Posts: 677 Thanks: 52 Thanked 56 Times in 53 Posts iTrader Rating: (1/100% )	Don't forget the strong possibility of corroded terminals at the connectors. Also, the insulation on the sensor wiring that is near the 02 sensor could be brittle, and cracked due to heat. I think you are on the right track. Good Luck.

07-16-2009, 04:46 AM	#3 (permalink)
mr2magic deutsch type skillz Join Date: Feb 2008 Location: Hannover, Germany Posts: 927 Thanks: 77 Thanked 36 Times in 33 Posts My Google Map iTrader Rating: (3/100% )	Check the resistance between all parts of the wiring O2 - O2 and O2 - ECU. You prolly have a wiring problem.

07-27-2009, 04:57 PM	#5 (permalink)
dirocyn Cage Fighter Join Date: Mar 2009 Posts: 133 Thanks: 6 Thanked 12 Times in 12 Posts iTrader Rating: (0/0% )	Should be a value between .2 and .7. ECU supplies .45. Here's an explanation of how it works, from people who know a lot more than I do. Oxygen Sensor Information