Willard

Greetings! new to the form, please be nice. I have a 99 miata with a check engine light. Codes read p1141 p1136 and p0140. Replaced front and rear 02 sensors, now im just getting the 1141 and 1136. The previous owner installed a jackson racing header, i donno if he could of extended the wire s but not connected them right. Also the rear 02 sensor was not connected and it looks as though he ripped the wires apart to disconnect it. (Stock exhaust system after header who does that) Im handy with a meter. Any advice? thanks
-willard

EricJ

Federal or California car???

So looking at this: Mazda Specific OBDII Trouble Codes
You have:
P1136 HO2S Bank 1 Sensor 1 Heater Circuit High Input
P1141 HO2S Bank 1 Sensor 2 Heater Circuit Low Input

Google the P0140.

I'd start off by going to Rock Auto and buying 2 new Denso 'Direct Fit' O2 sensors. The front and rear are different.
Plug them in and watch voltages via an ODBII reader. The front should bounce around 0.2v to 0.8v. Once warm the back should hover around 0.2v or less.

The header shouldn't change anything. I have a RB header, it's got a fitting for the sensor.

Now, if its a California car, ignore everything I've written.

Willard

I just typed up a nice long reply and deleted it somehow so here it is short and sweet.

Previous owner extended the front 02 sensor harness. With the 02 unplugged on the harness side i got 14v between the two heater wires. Also got .5 ohms between the 02 signal wire and 02 ground. Cut the ext. Harness Off and no longer have .5. Hopefully getting rid of that short solves it.

rwyatt365

If the PO did something with the wiring harness there's a 50% chance that they screwed up something - it's easy to do if you're not paying attention. Here is a link to a whole testing procedure to check the O2 circuit.

Willard

I redid the harness, and double checked the rear 02 wireing, still have the codes. Rwyatt thanks for the info ill read up on it. I found that i have a bp4y ecu (cali, i took it apart and checked for any burns looked ok). Will this affect anything?

Willard

Update: I found a short going from the rear 02 sensor heater circuit return to the pcm. I was getting voltage at the sensor but nothing @ the pcm. I ran a new wire and that got rid of the p1141 code. Also, i think i might be in the market for a new pcm. I was getting the code for high imput value on the front 02 heater circuit. I checked voltage at the pcm and was getting the 12v i needed, so i umplugged the 12v return and that got rid of that code. I drove the car for about a half an hour before getting a code for low imput value heater circuit front 02 sensor. Does that sound like i need a new pcm? I also got a new code for rear 02 sensor not giving the low voltage signal back to the ecu. I checked my live data and that verified that i wasn't getting a signal back to the pcm. i havnt looked into it yet but worse comes to worse i will run new wires, they are both new 02 sensors so...

Here are my new codes:
p1135: pedal position sensor A circuit intermittent
p1142: fuel restriction condition
p0140: O2 circuit sensor no activity bank1 sensor2

Wiring diagram i have been using: http://www.yorbalindamiata.com/images/wiring/99sys.pdf
02 sensors are on the 10th page

jakebaranek709

Just purchased a wideband o2 sensor to tag along to my speedy efi but now am realizing that the oem Miata plig is a 4 way and the o2 sensor I purchased is what to me is the regular type 4.9 lsu D shaped plug. Does anyone make a pigtail for these or can I just splice in to the old connector