2000 Maxima 124k Cali P0135 B1S1 O2 Heater Circuit

[chrisl67]

Problems started back in Febuary. Had car since 18k without any issues except O2 sensors, and the usual wear items (brakes, tires, etc)

P0135 Code, Engine was barely running.

My mechanic replaced B1S1 O2 sensor, code wasstill there.

Took to dealership. Diagnosed as bad Firewall (mid-pipe) Pre-cat.

I just finished replacing both pre-cats with Bosal parts. Carran better, but still hesitating. Replaced MAF with Napa direct replacementpart. Car runs like brand new! Code still pops up immediately after a full drive cycle (clear codes->drive->allow to cool->start) within 5-10 seconds of starting the MIL comes on P0135.

Took back to dealer for a diagnostic. (they found the bolt they had broken off (when they did the first diag on the pre-cat) the firewall side manifold flange that I didn't bother with, because the design of the gaskets prevented any leakage). They told me this was the problem with the car (exhaust leak). Quoted 538 to fix. Called me new years eve (all fixed). Picked up car, turned key, P0135.

My mechanic already tested all the 02 wiring from sensor to ECU and everything was fine.

The car has the original plugs, wires, and coils however it runs great, and given I've already dumped over 2k into it on this problem alone I don't want to replace anything else on a hunch.

My mechanic thinks it's a bad ECU. The dealership took the existing sensor out of the vehicle and tested it and said it's fine. I think this is the 3rd sensor I've put in the car trying to get this fixed.

I am beginning to believe that this is a bad ECU issue. I'm not happy about it, but that's what I'm beginning to believe is causing this never ending saga.

I will be taking it back to the dealer to have them fix the problem since they said it was an exhaust leak. I'm waiting for the "it's not a factory exhaust" explanation.

Could this be caused by coil, plugs, or bad TPS?

Thanks for any suggestions!

Happy New Year!

-Chris

[loystock]

I'm sorry but it appears to me that you have been ripped off. $2K is a lot of money. Your original mechanic has diagnosed it correctly - P0135 (Bank 1 Front Heated Sensor), probably after an OBD II scan. However, after replacing the O2 sensor, he did not verify its operation.

The dealership did such a bad job, IMO. You said they broke the bolt on the flange. When that happened, I presumed it caused an exhaust leak which caused the O2 sensor signal to be erratic. The O2 sensor voltage, under normal operation, swings between 0.45VDC (ideal fuel-air mix) to >0.6 (rich) and <0.3 (lean) several times per minute. Due to exhaust leak, the O2 sensor was exposed to higher than normal level of O2 from the atmosphere (lean signal) so there was little or no voltage swing at all, causing them to diagnose it as problem with the pre-cat. So replacing the pre-cat(s) will not fix the problem unless the leak has been fixed.

DTC P0135 - B1S1, indicates an abnormal current flow in the O2 sensor HEATER CIRCUIT, as seen by the ECM. This could be a problem with the O2 sensor (open heater element), harness (open/broken wiring) or ECM (unable to control heater power).

The 3-wire heated O2 sensor receives power thru the Ignition Switch while the ECM turns ON the heater (below 3600RPM Auto/4000RPM Manual) and OFF (at higher RPM). With the car at Idle, the O2 sensor heater must be turned on by the ECM. Speed info is provided by the Camshaft Position sensor to ECM.

The B1S1 O2 sensor is mounted on the Bank 1 vertical pipe with connector on top of the engine, rear, pax side. There are 3 wires/pins - Pin 1 is for Heater Control from ECM (L/Y-Blue wire with yellow stripe); Pin 2 is for the sensor signal (W-white wire); and Pin 3 is Power thru Ignition Switch (R/B-red with black stripe). The ground is just thru the shield on the harness.

The FSM recommends measuring the voltage from the ECM connector - Pin 119 (L/Y) and ECM ground. I believe you should also be able to check the voltage from the O2 sensor connector side (top of engine, rear). With engine at Idle, Pin 1 (L/Y) to ground should read 0-1VDC (heater turned ON by the ECM). At higher RPM (>3600/4000) the ECM turns OFF the heater so the voltage on Pin 1 should be the battery voltage (11.-14.7VDC).

Since the sensor tested OK, then the problem could be on the harness (open) or the ECM (no control thru Pin 119l). Check continuity of the harness between Pin 1 of the O2 sensor connector and Pin 119 of the ECM connector. If there is no continuity (open circuit, infinite resistance), there is a break somewhere in the harness. If continuity is good (0 or low resistance), the ECM is bad or the connector pin may be dirty, broken or 'pushed.'

In this situation, they can replace the O2 sensor a million times and it will never fix the problem

Here's a link to the FSM. Go to page EC-205 onwards (Engine Control System) for the wiring diagram and additional info.

http://www.nicoclub.com/FSM/maxima/2000/ec.pdf

[chrisl67]

Thanks Loystock!

My fault. I forgot to mention my mechanic fully tested the ECM harness connections to the sensor, and they came out good.

At this point I'd like to do a verification myself so I can sleep betterat night. If it weren't 25 out today I'd be out doing just that.

If the harness is bad, I'd be tempted to simply repair it, rather thanreplace (it's not an aircraft), but really don't want to revisit this..:P

If the computer is bad, I'm tempted to pay the dealer pricing simply because this has gone on so long, and at least it would be under warranty.

What's your opinion on a harness repair vs. replacement? Also, is replacing the computer a hassle, and is it worth the extra few hundred to have the dealer do it?

Thanks again for the helpfull feedback!

I'll post back as soon as I have a definitive diagnosis.

-Chris

[chrisl67]

Thanks Loystock!

My fault. I forgot to mention my mechanic fully tested the ECM harness connections to the sensor, and they came out good.

At this point I'd like to do a verification myself so I can sleep betterat night. If it weren't 25 out today I'd be out doing just that.

If the harness is bad, I'd be tempted to simply repair it, rather thanreplace (it's not an aircraft), but really don't want to revisit this..:P

If the computer is bad, I'm tempted to pay the dealer pricing simply because this has gone on so long, and at least it would be under warranty.

What's your opinion on a harness repair vs. replacement? Also, is replacing the computer a hassle, and is it worth the extra few hundred to have the dealer do it?

Thanks again for the helpfull feedback!

I'll post back as soon as I have a definitive diagnosis.

-Chris

[loystock]

The difficulty of replacing a harness depends on how many other harnesses are bundled with it and how they are routed in the cabin. Most likely, if there is a break, it should be close to the connector or maybe the problem itself is in the connector.

For as long as you keep the repair 'solid' and watertight, it should be OK. I have SWAMP (Special Wind and Moisture Problem) splices (from my days in the airline) that I used on 'as needed basis."

The OEM ECM can be expensive. One of NICO members have found a company that repairs ECM. You can check with him. Use the NICO SEARCH button and look for "Rodalt02."