# Code P1141 - Downstream 02 Sensor - Please help! **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** protege, mazda\ **Created:** [May 24, 2017, 9:21pm UTC](https://community.cartalk.com/t/code-p1141-downstream-02-sensor-please-help/104306 "2017-05-24T21:21:24Z")\ **Posts on this page:** 20\ **Page:** 4
**Author:** ![eddo](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/eddo/32/2594_2.png) [@eddo](https://community.cartalk.com/u/eddo)\ **Post date:** [May 18, 2018, 9:50pm UTC](https://community.cartalk.com/t/code-p1141-downstream-02-sensor-please-help/104306/63 "2018-05-18T21:50:16Z")
> [@mazda\_protege](#): > > Disconnect the HO2S connector. > Measure the resistance between the HO2S terminals C and D. Standard value: this is for testing the oxygen sensor itself. test across the terminals of the sensor- with it unplugged. ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [May 18, 2018, 10:40pm UTC](https://community.cartalk.com/t/code-p1141-downstream-02-sensor-please-help/104306/64 "2018-05-18T22:40:09Z")
For the 2000 Protégé LX w/1.6L DOHC, from what I’m seeing, the rear o2 sensor heater circuit spec is 15.7 ohms. The front sensor’s resistance depends on whether it is a Calif car or not. 5.6 ohm for Calif, 15.7 otherwise. If OP wants the exact spec, OP will have to secure a factory service manual or stop by a Mazda dealership shop and ask. ---
**Author:** ![mazda\_protege](https://avatars.discourse-cdn.com/v4/letter/m/dc4da7/32.png) [@mazda\_protege](https://community.cartalk.com/u/mazda_protege)\ **Post date:** [May 22, 2018, 12:58am UTC](https://community.cartalk.com/t/code-p1141-downstream-02-sensor-please-help/104306/65 "2018-05-22T00:58:22Z")
tHE heater spec is 15.7 Ohms? Then why does the autozone guide tell us to measure " 5-7 ohms across terminals c and d" (please read above) ? George, based on the information provided would you deem the 02 sensor as not functioning? ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [May 22, 2018, 1:44am UTC](https://community.cartalk.com/t/code-p1141-downstream-02-sensor-please-help/104306/66 "2018-05-22T01:44:19Z")
What resistances do you measure for the front and rear O2 sensor heaters? Is yours a Calif car? Or non-Calif? ---
**Author:** ![mazda\_protege](https://avatars.discourse-cdn.com/v4/letter/m/dc4da7/32.png) [@mazda\_protege](https://community.cartalk.com/u/mazda_protege)\ **Post date:** [May 22, 2018, 6:14am UTC](https://community.cartalk.com/t/code-p1141-downstream-02-sensor-please-help/104306/67 "2018-05-22T06:14:40Z")
Canadian car ie. non calif As I mentioned before for the rear I got 13.2 Ohms. Once I am able to tear apart the front one I will provide that reading. Thank You. ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [May 23, 2018, 1:13am UTC](https://community.cartalk.com/t/code-p1141-downstream-02-sensor-please-help/104306/68 "2018-05-23T01:13:42Z")
> [@mazda\_protege](#): > > As I mentioned before for the rear I got 13.2 Ohms. The spec I’m seeing says “approximately 15.7 ohms”. You measure 13.2 ohms, so the difference is 2.5 ohm. Your sensor is measuring 2.5/15.7 or 16% lower than the spec. I wouldn’t guess that is out of spec, but the spec doesn’t give any guidance on how far off it can be. So no way to tell for certain. You could go to an auto parts store and measure the resistances in 5 samples, so you’d have an idea how the resistances vary part to part. If they vary +/- 25 %, then you’d know yours is within spec most likely. You’ve got one more sample to measure anyway, the front sensor. fyi, the heater element is just a resistor, and electronics hobbyists know that resistors typically come in 1%, 5%, 10%, and 20% tolerance. The 20% tolerance version are the least expensive, but they still work fine in tolerance insensitive applications. I’d say a heater circuit is a tolerance insensitive application. ---
**Author:** ![mazda\_protege](https://avatars.discourse-cdn.com/v4/letter/m/dc4da7/32.png) [@mazda\_protege](https://community.cartalk.com/u/mazda_protege)\ **Post date:** [May 24, 2018, 3:26am UTC](https://community.cartalk.com/t/code-p1141-downstream-02-sensor-please-help/104306/69 "2018-05-24T03:26:18Z")
sooo what you trying to say is I should buy a resistor? a 2.5ohm one? and install it? ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [May 25, 2018, 1:16am UTC](https://community.cartalk.com/t/code-p1141-downstream-02-sensor-please-help/104306/71 "2018-05-25T01:16:34Z")
Measure the resistance of other sensor and post back what that one is. ---
**Author:** ![mazda\_protege](https://avatars.discourse-cdn.com/v4/letter/m/dc4da7/32.png) [@mazda\_protege](https://community.cartalk.com/u/mazda_protege)\ **Post date:** [May 25, 2018, 3:53am UTC](https://community.cartalk.com/t/code-p1141-downstream-02-sensor-please-help/104306/72 "2018-05-25T03:53:53Z")
Why would you assume the _front_ sensor would have the same readings as the _downstream_ sensor? @Deltron ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [May 26, 2018, 12:20am UTC](https://community.cartalk.com/t/code-p1141-downstream-02-sensor-please-help/104306/73 "2018-05-26T00:20:35Z")
That’s what the specs I found said. Except for the Calif versions of this car, the front and rear resistances have the same spec. ---
**Author:** ![mazda\_protege](https://avatars.discourse-cdn.com/v4/letter/m/dc4da7/32.png) [@mazda\_protege](https://community.cartalk.com/u/mazda_protege)\ **Post date:** [May 26, 2018, 5:45am UTC](https://community.cartalk.com/t/code-p1141-downstream-02-sensor-please-help/104306/74 "2018-05-26T05:45:34Z")
Going to the junk yard tommorrow to pull off downstream o2 sensors. What tools do I need? They are free. ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [May 26, 2018, 10:31pm UTC](https://community.cartalk.com/t/code-p1141-downstream-02-sensor-please-help/104306/75 "2018-05-26T22:31:50Z")
> [@mazda\_protege](#): > > What tools do I need? > **[Mazda - OEMDTC](https://mazda.oemdtc.com)** > > Mazda Recalls, Technical Service Bulletins TSB's, Diagnostic & Repair Tips ---
**Author:** ![mazda\_protege](https://avatars.discourse-cdn.com/v4/letter/m/dc4da7/32.png) [@mazda\_protege](https://community.cartalk.com/u/mazda_protege)\ **Post date:** [May 28, 2018, 11:17pm UTC](https://community.cartalk.com/t/code-p1141-downstream-02-sensor-please-help/104306/76 "2018-05-28T23:17:23Z")
Thanks Went to the junk yard earlier…all the 02 sensors from the proteges were removed! vultures scour the junk yard for parts and then resell them at a profit. Anyway, I measured the front o2 sensor: - 12V on the lower left PIN - 20ohms across the two black wires (different reading than the 13 ohms on the downstream 02) This was unplugged. @Deltron @George_San_Jose1 So its the sensor or the wiring? ---
**Author:** ![VOLVO-V70](https://avatars.discourse-cdn.com/v4/letter/v/8e8cbc/32.png) [@VOLVO-V70](https://community.cartalk.com/u/VOLVO-V70)\ **Post date:** [May 29, 2018, 12:24am UTC](https://community.cartalk.com/t/code-p1141-downstream-02-sensor-please-help/104306/77 "2018-05-29T00:24:43Z")
I think Deltron has left the building as he has not posted in over a month. ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [May 30, 2018, 2:18am UTC](https://community.cartalk.com/t/code-p1141-downstream-02-sensor-please-help/104306/78 "2018-05-30T02:18:46Z")
The fact that the front sensor measures 20 ohms and the rear only measures 13 ohms (when the specs say they should be the same) & you got proper voltage at the harness ok to both sensors suggests maybe there is indeed a problem with that rear sensor. I think at this point , if this was my car problem, I’d probably replace the rear sensor and see if that solved the diagnostic code & engine warning light problem. I should say that before doing that – just saying what I’d do – I’d figure out a way to verify the voltage with the sensor plugged in is the same too, before ponying up for a replacement sensor. Another idea is to swap the sensors and see if the problem switched from rear to front. But that’s probably more trouble that it is worth, given the difficulty of diddling with an 18 year old exhaust system. ---
**Author:** ![thegreendrag0n](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/thegreendrag0n/32/9265_2.png) [@thegreendrag0n](https://community.cartalk.com/u/thegreendrag0n)\ **Post date:** [May 30, 2018, 12:45pm UTC](https://community.cartalk.com/t/code-p1141-downstream-02-sensor-please-help/104306/79 "2018-05-30T12:45:24Z")
Power = Squared(Voltage) / Resistance. Running voltage can be considered around 14 Volts. The difference between 20 ohm and 13 ohm is in ability for the internal sensor heater to draw 9.8W (20 ohm) and 15W (13 ohm) of power respectively. It will not be exact, as resistance will change with temperature change, but it illustrates the point. For me it would be a good reason to scratch my head and think “well, if ECM complains it can not heat the sensor and I know sensor is 35% low on heater power, so maybe ECM has a point?” Replace that goddamned sensor 🙂 ---
**Author:** ![mazda\_protege](https://avatars.discourse-cdn.com/v4/letter/m/dc4da7/32.png) [@mazda\_protege](https://community.cartalk.com/u/mazda_protege)\ **Post date:** [May 31, 2018, 12:07am UTC](https://community.cartalk.com/t/code-p1141-downstream-02-sensor-please-help/104306/80 "2018-05-31T00:07:58Z")
called mazda dealership…they say the front and rear sensors are not interchangeable! ---
**Author:** ![VOLVO-V70](https://avatars.discourse-cdn.com/v4/letter/v/8e8cbc/32.png) [@VOLVO-V70](https://community.cartalk.com/u/VOLVO-V70)\ **Post date:** [May 31, 2018, 12:13am UTC](https://community.cartalk.com/t/code-p1141-downstream-02-sensor-please-help/104306/81 "2018-05-31T00:13:30Z")
For crying out loud , started thread May of 2017 - 77 posts . Just take the thing some place and have it fixed. ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [May 31, 2018, 12:39am UTC](https://community.cartalk.com/t/code-p1141-downstream-02-sensor-please-help/104306/82 "2018-05-31T00:39:37Z")
> [@mazda\_protege](#): > > called mazda dealership…they say the front and rear sensors are not interchangeable! That’s correct. At least from what I see, they have different part numbers. The front one starts with ZM01, the rear with ZM02. But the resistance spec is the same front/rear. 15.7 ohms for both. ( The Calif version part number for the front starts with ZM03. ) ---
**Author:** ![Nevada\_545](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/nevada_545/32/41232_2.png) [@Nevada\_545](https://community.cartalk.com/u/Nevada_545)\ **Post date:** [May 31, 2018, 12:50am UTC](https://community.cartalk.com/t/code-p1141-downstream-02-sensor-please-help/104306/83 "2018-05-31T00:50:26Z")
Most are not interchangeable, front and rear oxygen sensors have different cord lengths and different connectors to keep you from plugging them into the wrong connector. [Previous page](https://community.cartalk.com/t/code-p1141-downstream-02-sensor-please-help/104306.md?page=3) [Next page](https://community.cartalk.com/t/code-p1141-downstream-02-sensor-please-help/104306.md?page=5)