# P1296 & P0420 codes and fix support.



## civilrock (Oct 15, 2010)

History:
1. check engine light has come on 3 times now.
2. went to parts store to borrow OBD code reader. got P1296 and P0420 (bank 1)
3. searched here and found several threads on the subject.
4. called dealer and there are no recalls on VIN. (there is one for the VR6)
4. P1296 is probably the Coolant Temp Sensor. (get the green top)
5. P0420 is the front O2 sensor.
6. Local VW parts shop has both. CTS- $19, O2- $79. ($37 and $207 at the dealer)

2001 Golf 2.0L with 75k miles.

Before I dole out $100 on parts and get my hands dirty, did I read this correctly and is this the proper fix?

Thanks!
-Kevin


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## greyhare (Dec 24, 2003)

P1296 VAG17704 Cooling system malfunction: May be the ECT. Can you get a scanner to keep over night? First thing before starting the car check the IAT and ECT; if they are not close the ECT is probably bad.

P0420 VAG16804 Catalyst system,Bank 1 efficiency below threshold. This is usually the Cat or the post Cat O2.


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## civilrock (Oct 15, 2010)

greyhare said:


> P1296 VAG17704 Cooling system malfunction: May be the ECT. Can you get a scanner to keep over night? First thing before starting the car check the IAT and ECT; if they are not close the ECT is probably bad.


 That sounds easy enough. They should both be at the ambient temp when the engine is cold eh? I'll see if they'll lend me the scanner. 


greyhare said:


> P0420 VAG16804 Catalyst system,Bank 1 efficiency below threshold. This is usually the Cat or the post Cat O2.


So how would a guy determine which O2 sensor or if it's the Cat? 

BTW, thanks so much for the answers! I really love solving problems without a bunch of wasted moves (expenditures).

-Kevin


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## rommeldawg (May 25, 2009)

actually that is telling you cat is bad... with live data you can read the output of the first and second O2 sensors on that bank to verify the cat is dead or dying ... but its more then likely the cat


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## civilrock (Oct 15, 2010)

*Front O2 Sensor removal?*

I did some internet searching on how to test an O2 sensor and how to tell if the cat is bad. I think I can handle that. BUT, do I need a special tool to get the front O2 sensor out? Before I start taking the heat shield off, I thought I might ask since it's not in an easy spot.









I talked to the PO about the CTS (coolant temp sensor) and she had it replaced just a few years ago. (actually I remember because I helped her fix it when it was leaking). Maybe the new one is faulty? donno.


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## civilrock (Oct 15, 2010)

*answered my own questions*

I should just look around before I ask these questions. Heading to Harbor Freight right now. They have the right tool for $7.








http://www.harborfreight.com/3-8-eighth-inch-oxygen-sensor-socket-95045.html

I'm going to get a Non-contact Laser Thermometer too while I'm there.


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## rëvö ëvöm (Dec 8, 2010)

*I recently had similar issues*

Recently my car was throwing similar codes. I had recently replace both O2 sensors and the cat. I started getting the code P1296. At first I thought it was a bad CTS and thermostat. It turned out to be a bad water pump. I would check there if you are coming up on having to replace the timing belt.


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## civilrock (Oct 15, 2010)

Shade tree mechanic's results.

Cat test 1 - find the difference of the temp before and after the cat.
The front was about 390 deg F and the back was about 320. doesn't really seem too far apart.

Cat test 2 - measure the pressure at the Pre-cat O2 sensor.
My compression tester didn't move at all. The first mark is 20psi, but the needle didn't even move. Again, not enough for a bad cat?

Next I was going to put the tip of the sensor in a propane flame, should be 0.1V out of the flame, and closer to 0.9V in the flame. But there's 5 wires coming off the sensor. Black, red, yellow, grey, and yellow. Black is ground. I'm guessing red is for the heater? don't know which one is the right one to test out of the rest.

I'm wondering if all this playing around is not really sophisticated enough to really figure out what's wrong. Should I borrow a scan tool and follow a guide to let the car tell me what's really wrong?

When does the timing belt need to be changed? I'm at 74k even. I thought it was 100k? 

I like to tackle this stuff even if I screw it up. I'd rather learn that pay someone. 
Thanks for all your help, all of you.

-Kevin


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## chrischeez (Nov 29, 2007)

p1296 occurs when the coolant temp switch reads the coolant has reached a specified temp in the required time frame. this code is more often than not IME, the thermostat. when you have the thermostat out you can feel the impeller in the back corner of the hole the thermostat was in,and if it spins or wiggles or you can feel a crack, or if you can tell if it has a plastic impeller, which all dealer pumps and cheap aftermarket pumps have, you should probably just replace it with a metal one if you can swing it. but for sure if its broken, but if it was, your heat would suck and your car would overheat.if your heat rocks, its most likely your sensor. does your temp gauge work? does it go all the way up to half?


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## civilrock (Oct 15, 2010)

I'll check or replace the thermostat. I was thinking that I'd just replace the water pump this spring when I was planning on doing the timing belt. 

The temp gauge works. don't know how accurate it is, but temp comes up as it should then stays right in the middle all the time. heat works perfect. 

Maybe I got a bad sensor, but it was replaced about 2yrs ago. I really appreciate the ideas. 

since I put it all back together, the light has gone off, and not come back on. It has only come on first thing when I start it up cold. I feel a little bump like it's about to die, then the light comes on. Other than that, there's almost zero other effects. same MPG, same everything. 

Cheers.


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## nosborn94 (Feb 7, 2010)

Did the issue ever come back? Or did you make anymore head way on this? I got 17704 and 16804 just like you recently


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