# Troubleshooting pre-cat O2 sensor (DTC P0130) using OBD-II scanner in BBW engine



## muxspace (Jul 2, 2012)

Hello, I have a 2004 Jetta 2.0 with the BBW engine. The ECM is telling me that the oxygen sensor in bank 1, sensor 1 (pre-cat) has a circuit malfunction (P0130). I've used two different code readers, which both give the same trouble code. I replaced the O2 sensor with the Bosch 17085 and still have the same code appearing (after erasing it and driving around for 10 minutes). 

After replacing the sensor I tried the following:
1. Check for vacuum hose leaks. No obvious leaks were present. I also read that if this is the case, there is usually a companion DTC indicating low pressure or some related problem.
2. Checking resistance of heater element in original O2 sensor (~3.4 ohms). From what I've read, this rules out that the heater is bad but the sensor could still be bad.
3. Connect to ECM with my computer, and read data via ELM327 interface. If I send PID 0114 (bank1, sensor 1 voltage) I get a NO DATA response. Bank 1 sensor 2 (0115) and bank 1 sensor 3 (0116) both give me values back. I read that since the pre-cat sensor is wide band, you can't measure the voltage since it is generating a current instead. This seems to be corroborated by the results of the 0100 PID request which didn't have the bit for 0114 set. There are other PIDs for lambda, which I understand to be the output of a wide band sensor. Querying these PIDs (0124, 0125) give me the same NO DATA response.

So I'm running out of ideas. I read that you can check the connections with the ECM, which requires pulling out the wiper assembly and shunting an ammeter in there. Anybody try this? 

What other options do I have aside from replacing the O2 sensor again? Anybody know in a working BBW MKIV whether PIDs 0114 or 0124 provide actual data? Any help greatly appreciated.


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## Anony00GT (Mar 6, 2002)

I'm not familiar with the scan tool you're using, so I can't answer your question about PID numbers. VCDS (or dealer VAS) is the only reliable and correct tool for scanning this car, generic OBDII tools provide limited (and often inaccurate) data when scanning VW's.

My parts catalog is showing Bosch 17361 as the proper sensor of Bank 1 Sensor 1 on BBW. 17085 is for a BEV. Install the correct sensor, clear codes, see what happens.


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## muxspace (Jul 2, 2012)

Hmm, that's weird. I could've sworn I verified that this was compatible with BBW, but looking on the Amazon page, BBW is not on that list. I hope this is simply just a parts fail and nothing more.

ELM327 is the IC for interpreting OBD signals. This is the chip used in many scan tools. Regarding VCDS do you know what protocol it uses to connect to the ECM? The ELM327 indicates that the protocol used is ISO 9141-2. Is VCDS using something different?


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## Anony00GT (Mar 6, 2002)

VCDS uses VW's KWP protocols on pre-CAN models. It's essentially the same tool that the dealership uses at the OE level. It also has 100% bidirectional capability for running output tests, coding, and basic settings (ie, actively testing things like Lambda and O2 sensors). Your ISO protocol offers 0% bidirectional capability.

Generic OBDII has many shortfalls, especially on VAG vehicles. Here is an example of a major code discrepancy OBDII vs VCDS that I happened across just a couple days ago, and it's all too common:

http://forums.vwvortex.com/showthread.php?5733659-please-can-someone-help-me


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## muxspace (Jul 2, 2012)

Thanks for the detail. The bidirectional capability certainly sounds useful. It turns out that the ELM327 supports KWP as well, so maybe it can perform the same functions. 

Regarding the generic OBD-II scan tools, thanks for pointing this out, but isn't this a different situation? The codes in the P0xxx range are government regulated so must conform to the SAE standards, while codes in the P1xxx are manufacturer-specific. So for my case, P0130 is reported the same, whereas P1300 says something different. Presumably the Bentley code table is the correct one to reference in lieu of the generic codes: http://www.bentleypublishers.com/tech/vw/vw.dtc.table.htm


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## Anony00GT (Mar 6, 2002)

It does not have the ability to do what VCDS does, not even close.

You can read all the books about federally regulated OBDII, blah blah blah. Try this: Use VCDS (or an OE scan tool for any manufacturer) and you'll see how bad OBDII really is.

As for the codes under P1000, the answer is yes and no. See the same thread I referenced above, P0440 and P0455 are EVAP, yes. The actual definitions given by AutoZone and VAG vary slightly, but the logic the ECU uses to flag each code is slightly different than the code definition suggests, even the definition on the link you provided.

In your case, the codes do match: fault in heater circuit B1S1. Install the correct sensor and clear the code, drive as necessary to set monitors.


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## muxspace (Jul 2, 2012)

Anony00GT said:


> In your case, the codes do match: fault in heater circuit B1S1. Install the correct sensor and clear the code, drive as necessary to set monitors.


Hi, I installed the oxygen sensor Bosch 17361 and erased the trouble codes. After about 5 minutes I get the same trouble code appearing (P0130). Any other suggestions?


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## Anony00GT (Mar 6, 2002)

Check the circuit between then O2 sensor and ECU, refer to wiring diagrams. If a problem is found, repair ASAP.

Scan with VCDS to make sure no additional codes are present (TPS or APP-related codes), also to verify the accuracy of the code you're pulling.

A short in the O2 heater circuit can burn down the ECU in these cars, creating throttle issues as well as O2 sensor issues, and generic scan tools don't always pull all the codes.


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## muxspace (Jul 2, 2012)

What should I check for in the circuit? I have the Bentley books for the MkIV so I have the general schematic (No. 86/10 in Volume 2), but it doesn't really indicate anything about what signals to expect from the different connections to the ECU.


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## Anony00GT (Mar 6, 2002)

Just check the integrity of the wires with an ohmmeter. Use the WD in the Bentley for pin locations on the ecu.


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