Re-occurring P1135 engine code on Miata 2000 above 4000 RPM

P1135 H02S11 Heater Circuit Low (From my scanner Mazda code list) DTC 1135 from 99 Miata Shop Manual PCM voltage is below 5.8v when no power is supplied during 322-327 sec after engine start to heated front O2 sensor.(From Shop Manual) ??? if no power is supplied, how can it have 5.8 v or any voltage for that matter??

Possible causes Wrong sensor heater resistance heater value or shorting wire to sensor? I'd (on a 99) check the voltage between ECU(PCM) pin 1U and the ignition switch and the sensor C pin Also, grounding may be a problem. The harness side of the connector pin layout is Long index to the top, short index on bottom and each side. ____

- A-C- B-D -

I would guess that the PCM does get a signal from the sensor (it says PCM voltage,) while there is no heater voltage (or evidence of one, maybe.) Or maybe the opposite way around.

Yes, or the wiring harness, maybe. The OP says he has replaced the oxygen sensor with a new Mazda unit. Maybe the problem was not with the O2 sensor to start with?

I don't know about a 99, but on a 96 that is one dirty, hot area. Come to think of it, I guess it is hot on any car. :)

Vibration makes poor contact unusable. PCM takes offense at being slighted. Problem solved except for confirmation. :)

OK, I do not really have a clue, but follow on discussion was requested. :))

Leon

Update on the original posting.

Work has interfered with diversions, so I have not devoted much time to this lately. The Miata is my toy car, so it is aging nicely in the garage.

Before I got distracted, I did spray cleaned (with connector cleaner) and reseted two harness connectors that I think are on the harness line from the O2 sensor to some actuator that I think it may be related to the VICS stuff. This is all from the back side of the cams cover to the rear top side right side of the engine. I do not have schematics, so I do not know what connects to what (computer, actuator, etc.). No improvement. The connectors are well set and secured. I would venture to guess that contact discontinuity due to vibration is not likely in this

2000 configuration. It is hot in the area behind the block, but I can trigger the problem with the engine block cold if I rev. it up.

The problem does not occur at RPM lowers than 4500 or 5000. I could run the car for miles at the lower RPMs without triggering the engine light to go off.

My guess it that the O2 sensor error is a red herring, but I have no idea what is signal flow in this engine management. So, I will break out the electrical multimeter next to check wiring continuity and levels. If any one knows of a good technical descriptions of engine management for Mazda, it would be welcome.

Thanks for the replies so far. I know the answer will be trivial once it is revealed.

Well, let's FIX that, OK?

Scroll down until you see Wiring Diagrams toward the bottom of the page, click on it, select your year and get them. You'll need Adobe Reader to read them.

Interesting thread. I came here to post a question and started reading this one :-).

Bottom line, will the car pass your local smog test?? And does the light go out when you are under that 4000 RPM threshold??

First reply: Many thanks to "xs11e" for the link to

!!It prints clearly despite the small fonts.I assume that a text description of the operations related to diagram B-1a (Engine Control System) on page Z-18 of file 001_2000wire.pdf would be too much to ask in life? :-)I suspect that a mode transition at high RPM (solenoids to VICS, ignition coil 1 vs 2 use, etc.) may be at fault here. It may be that the O2 sensor is (and was) actually working right, but the ignition process saturates the sensor on those peak rev-up instants ??????Thanks again.

Second reply: The car is not likely to pass smog test since on the bi-annual test next year the car has to go on the "thredmill". Any instantaneous reving-up of the engine will set the engine light, even if the cause it not part of the test cycle.

The light gets set by the event and it has to be cleared manually (via the reader, BTN1 fuse removal or ground battery disconnect). I suspect after the RPM go down, there is no instantaneous error condition, but I do not know because the engine light does not auto-clear in my case. As I understand it, the implementation of many engine light faults auto-clears only after a large number (e.g., >40) of engine on-start-off cycles with no faults.

I drove 80 miles yesterday not reving the engine past 4300 RPM or so. No event. Today I instantaneously reved the engine to about 4800 RPM or so and it triggered. However, I rather look at traffic on the freeway than my tach when this happens, so I may not have the numbers exactly at the maximum levels. It is very repeatable.

rm

Page 13 of file oodtc.pdf at

a list of possible causes and test sequence. Thanks.

XS11E wrote:

Does the VIC rod move when the engine is started?

In reality, the ECU should care less if the VICS actually operates, as long as the solenoid operates. There is no sensor that can tell if long or short passages are selected.

My book shows operation at ~5300, not 4800 (I really don't know what the reality is.

I'd look to see if the battery voltage is at least 14.2 volts or so when the problem occurs.

Unfortunately, the service manual has a long sequence using the dealer tester to force testing modes to diagnose VICS problems.

==> Yes, it does move.

==> Problem happens at open throttle near 4500 RPM onwards. It is an RPM and throttle combination, the best I can tell now after a few more runs. ==> Air filter, plugs and plug cables are relatively new ( Fuel filter is original (12000 miles before recommended change), but there is no hesitation at open throttle.

==> Can not measure it when the problem occurs, but it appears nominal engine off and engine on at idle. Battery is relatively new and there is no charge problem.

==> The new front O2 sensor heater resistances is nominal (in retrospect inspection, so was the old). Voltage level to the heater element is nominal. I have not gotten to the connectors to the PCM yet.

==> The car appears to be working normally otherwise, even at full throttle. I am not sure that there is even an emission problem since it is just an instantaneous fault that appears not to occur over 95%+ of the driving time. The error code is still P1135. I have a while until I have to inspect it again. I may have to take it to Mazda service so that they can fix their own system and/or get it to pass inspection.

==> I do not have a good history with Mazda service departments. So I was trying to avoid that experience again. It took many visits around

2001 to get them to fix a grinding and blocking 6-speed transmission on this same car that I bought new. They tried to fix it the first time and that was worst. Finally they replaced the gear box. They were very reluctant to approve any warranty work. It may be that some harness cable to the PCM got pinched due to these repairs and they finally failed. Who knows. Mazda makes some interesting cars, but their service has been mainly concerned with reducing cost to them rather than maintaining customer satisfaction, at least in my prior warranty repair case. However, once the customer is paying, the amount of work they are willing to bill is tops. Other than for the transmission being bad from the factory at the onset, I had no other non-maintenance repairs until now (48,000 miles). My only regret is that I may have to deal with Mazda service again. That is why I was trying at least to troubleshoot the problem.

==> Thanks to all for the suggestions. When I get a final resolution, I will post the outcome.

A good smog test AND repair center that you might know and trust may be your best bet

Well, I can feel your pain for having a problem. BUT, I can't feel the the same pain that you have for a "dealer" that somehow people run into. I live in Seattle WA. One of the dealers we have here is the "First" dealer for Mazda in the US. I had a head gasket problem on my '91. It was 1994 and way out of time and milage, but they replaced it. 4 years (yes 4 years) later, it started to leak again. I took it in and after they had the car for 2 days, ( a free loaner car to me ) they said that they would relplace the gasket at no charge. Sooooooo, you see, it is hard for me to think all dealer service is bad.

I hope you can find a dealer that will treat you well and fix your problems.

Bruce Bing '03 LS

4000 RPMs, > the engine light, the P1135 code and 2 sensor indicators (whatever that > is) come up up again. I have searched the net for equivalent failure > modes and I can find some cases when this has occurred, but it appears > that people have not posted the subsequent solution. The engine does not > run rough at all at any RPM and there is no lost of engine power. The

confusing, >

since other failures associated with the coil, etc. triggered other

48,000 miles, one year old NGK plugs and > cables, good battery, everything else is original)

Rha: I am currently having the same problem. Just purchased a

2000 Miata and I got two codes last week, a PO300 and P1135. Fixed the plug wiring and no more PO300, but I can't keep the car from showing a P1135 once I go WOT. It appears to be the same problems you were having back in '07. I am curious on if you found a final diagnosis, was it a bad ground? I've replaced the plugs and plug wires. 'm tempted to just take it in to the miata dealer but will be getting my hands on a jack next week so I think I'll wait to look at the rear O2 sensor wiring. Let me know if you have any input. Thanks for your time.