Sporadical P0135 code

I need your help!
I've got a car with an AZD engine (1.6l 16V petrol) and I got P0135 code time to time.. Sometimes after 20..30 seconds after I started the engine, sometimes when on road for hours.. Sometimes it comes back in minutes, sometimes it won't show up for 2..3 weeks..

The sensor has been changed already, it is a 5 wire NTK sensor (AFR sensor, not 4 fire oxygen sensor).

In theory the heater receives the + from the battery/alternator via the fuel pump relay (fixme if not) and the ECU is grounding it with PCM signal, the duty cycle depends on the current flow, current flow depends on the heater resistance - hence the ECU knows the temperature.

From the manuals and various Internet resources I figured out that the P0135 code will set when the ECU on the sensor's heater circuit senses 0.2A or below or 2A or above - or when it takes too much time to reach the operating temperature (so it's resistance not increasing as rapidly as it has been programmed to the ECU).
I measured the resistance of the sensor heater element when the engine was cold (this morning) and it is 3.5Ohms which is correct according to some forum threads and other links.. With ignition on/engine off I measured the voltage between the heater circuit + and - wires coming from the ECU and I measured 9.85V. So, when I connect the wires it will draw 2.8A and the heater element starting to warm.. and it's resistance is starting to increase.. and the current will decrease.. and be within 0.2A and 2A so no code will set.. in theory.

So, the sensor is "new" (used it for ~18.000km already..) but showing this error since around it's fitting to the car (after 1 months or so), I've checked the fuse table (replaced all fuses which have engine icon), grounding is okay (measured the resistance and voltage drop between the heater - wire and the battery - and car chassis and engine head ground). I'm not sure that the resistance is okay but it seems. I'm not sure about the heater circuit voltage neither becuase most forums says it should be around 12V. Battery voltage is 12.4, alternator voltage is around 14.2 but when the car warmed up it goes down to around 13.4V (the alternator has a temperature compensated voltage regulator so as far as I know it is okay as well.). I used a DVOM for these measures, unfortunately I haven't got a scope.

What can be the issue then and how can I remediate it? It's so sporadic.. I did not cleared the code I got today yet and when it's been set the fuel system status went to "open/sys fail" immediately - but after a couple of seconds (20..30s) it went back to "closed loop" again - so I'm not sure what is going on.. will the code reset itself / deleted by the ECU after a couple of starts?



(If my english is not readable/understandable or something let me know, it's my second language. Thank you!)

have you cleared the STORED & PENDING codes ?

What was the make of the new sensor ?

Hi Niall,


Yes, I cleared all kind of codes (did it with OBDII readers and VAG-COM and VCDS), several times.
The sensor is an NTK sensor (LZA11-V4 or NTK 1842) and these sites are telling me that it is compatible:
1 X NGK LAMBDA SENSOR LZA11-V4 1842
LZA11-V4 | NGK Oxygen Sensor 1842 | Lambda Probe
NGK Lambda Sensor (1842) buy cheap online
And this converter says the same as well:
http://www.oxygensensor-crossreferen...t/ntk/LZA11-V4

Well, I would say that I would replace the sensor.

If you have kept the receipt ,then just exchange it. Plenty sensors break or are broken when new, whilst its a pain ; its worth remembering when you fir them you tend to think it must be something else.

As its sporadic,its entirely up to you if you can put up with it or not

Thank you for the idea and advice, much appreciate it.

Anyone else with any ideas before I change the AFR sensor that ran only ~20.000km and one year old only?
Crasher? Any advice on what else to check? Wiring diagram? Fuel pump relay can be related?

Something is wrong because according to the VAG workshop system the AZD engine cannot generate

16519 (P0135) Bank 1 Senor 1(G39) - Heater circuit malfunction

as it is not on the list of possible codes although that could be wrong as the matching code for B1S2 P0141 is listed.

Check the brown and blue/yellow wires at the six pin plug on the gearbox for breaks or corrosion to the pins.

Thank you, Crasher, for the quick answer!
The connector and all pins are free of corrosion.

What I found is that probably the naming is weird to me:
Z19 - Lambda probe heater
Z29 - Lambda probe 1 heater, downstream of catalytic converter
Why it is referring to Z29 (downstream) sensor as "1"?
P0135 means B1S1 but according to the naming it is probably
not for the upstream but for the downstream sensors? :S

G39 is the pre cat sensor, B1S1 and Z19 is the heater for this, Z29 is the heater for G130 which is B1S2, the post cat sensor.

B1 = Bank 1 (but it has only 1 bank!)

S1 = Sensor 1

S2 = Sensor 2

Check for battery voltage across pins T6q/1 and T6q/2 with the engine running

NGK sensors are referred to by the technical components operations brand name NTK. The probe was originally VAG part number 036 906 262 E which changed to 036 906 262 J and this is an NTK LZA11-V4 or the quick reference number 1842 so what you have fitted is technically correct. However, a few years ago I did the same thing on a Passat and in the end found that the NTK’s heater resistance was way off what the original Bosch one was and the ECU just would not accept it, a Bosch part cured the problem so you could have a similar problem. VW do not provide a specification for the resistance of Z19.

http://i222.photobucket.com/albums/d...psaxokuyw1.jpg

Yes, I saw the thread of the Passat and I will check the voltage between T6q/1 and T6q/2 with the engine running tomorrow.

Can you do me a favor? Where exactly E7 is and how is it look like?

According to the diagram - if I'm not mistaken - E7 is a kind of junction point and not only one thing is connected to it but more - the fuel pump relay, the pre- and postcatalyst lambda sensor and the activated charcoal filter solenoid and fuse #43. These electrical loads are connected parallelly as I see and if I measure 9.85V on the Z19 then I must read the same voltage on the others' blue/yellow cables as well compared to the battery negative connection - if the quality of the cables and connections are the same to all endpoint, right?

The positive wire "entry point" for these electrical loads is the fuse so I must check the voltage on the fuse as well I think to check is there any voltage drop.. But how E7 and fuse #43 is connected to the battery?

So, I measured the voltages with running, warm engine:
Fuse #43 to the chassis ground (both ends): 12.15V
B1S1 Z19 heater circuit - between brown and blue/yellow wires (T6/q1 and q2): 12.14V

I started Torque Pro and checked the Mode $6 monitors, everything is green, completed.
Then checked the measured value reports and found something odd:

Test report:
------------------
TID:$01 CID:$06
- Rich to Lean sensor threshold voltage(constant)
Max: 5,000
Test result value: 3,333
PASS
----
TID:$02 CID:$0e
- Lean to Rich sensor threshold voltage(constant)
Max: 1,000
Test result value: 454
PASS
----
TID:$02 CID:$10
- Lean to Rich sensor threshold voltage(constant)
Max: 510
Test result value: 454
PASS
----
TID:$02 CID:$11
- Lean to Rich sensor threshold voltage(constant)
Min: 390
Test result value: 454
PASS
----
TID:$02 CID:$12
- Lean to Rich sensor threshold voltage(constant)
Max: 956
Test result value: 761
PASS
----
TID:$02 CID:$14
- Lean to Rich sensor threshold voltage(constant)
Min: 700
Test result value: 888
PASS
----
TID:$02 CID:$1f
- Lean to Rich sensor threshold voltage(constant)
Min: 100
Test result value: 455
PASS
----
TID:$05 CID:$0e
- Rich to Lean sensor switch time(calculated)
Max: 200
Test result value: 9,640
FAIL
----
TID:$06 CID:$05
- Lean to Rich sensor switch time(calculated)
Max: 4,300
Test result value: 3,828
PASS
----
TID:$06 CID:$06
- Lean to Rich sensor switch time(calculated)
Min: 3,400
Test result value: 3,828
PASS
----
TID:$06 CID:$07
- Lean to Rich sensor switch time(calculated)
Max: 1,300
Test result value: 456
PASS
----
TID:$06 CID:$09
- Lean to Rich sensor switch time(calculated)
Max: 935
Test result value: 767
PASS
----
TID:$06 CID:$0a
- Lean to Rich sensor switch time(calculated)
Min: 650
Test result value: 767
PASS
----

As you can see TID:$05 CID:$0e has failed and I tried to reset it and let it measured again by the ECU several times but always fails. The most interesting thing in this is: the OBDII readyness for O2 sensor is always complete/pass. According to the Torque Pro tests this test (TID:$05 CID:$0e) is the calculated rich to Lean sensor switch time - but this is an AFR sensor, not a simple, 4 wire O2, so this is confusing to me as well. Is there any documentation of the TIDs and CIDs? Or it is something secret? How come Mode 6 test 5 component 0x0E (decimal 14) fails but the readyness of the O2 is always green/pass? :\