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2010 B8 A4 Avant 2.0 TDI 120HP
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Discussion Starter · #1 ·
Hello fellas.

Recently my golf started to use A LOT more fuel than normal. I'll explain.

Usually it sat around 7.5L/100km (32mpg) or less on country roads / highway. Not weird considering the car is now 22 years old. When new it was rated 6L/100km.
My guess is that it is a bit more efficient, considering I got that driving from Berlin to Oslo (around 1700km) averaging around 130-140km/h, not exactly the optimal speed for this engine.

Lately however it has increased to using around 1.0L per 100km (24mpg) in the same driving conditions. A 30% increase. This is alarming to me as it is a small 1.6L petrol and I might as well drive a fat pickup and get the same fuel efficiency. I've tried replacing the fuel filter (original from VW dealer, not aftermarket,) and I've replaced the oil as it was past schedule. That did not seem to improve anything. Spark plugs are well within service intervals, same with air filter.

I have a slight suspicion it is related to the oil change, but I am not sure if the fuel economy changed before or after the oil change. I did a full flush: Drained oil, filled car with "cleaning oil", idled for 10 minutes, then drained and replaced oil and oil filter.

Seemingly related symptoms include:
  • Sometimes the throttle is very responsive, other times it kind of hiccups. The cars performance (or how hard I have to press the throttle) seems to be related to this as well.
  • Idle rev sometimes hangs at about 1600rpm after start, but sometimes doesn't. The normal cold start high rev is 1100-1200rpm.
  • Driving uphill on freeways the car sometimes seems to "slip," as either as if the clutch slips, or the fuel system is cut off for a very short time.

Other unrelated (as far as I know) issues:
  • During the winter the ABS sensor sometimes gets messy and often disables ABS, or even triggers a brake warning light flashing.
  • Coolant level in the car has slightly been decreasing the past 6 months. Temperature still consistent at 90 deg at all times when driving.
  • Some dash lamps seem to not work. E.g. my windshield washer fluid reservoir has a level sensor, but it never triggers. I believe the check engine lamp still works. It also has a display that does not show anything.

My guess is this could be a sensor issue, perhaps exhaust or intake related, or a problem with the injectors, but I have no experience with issues like this so I am in now way certain.
 

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Have you scanned for car for codes? Increased fuel consumption may vary on a couple of things such as MAF, O2 sensors and a bunch of misc sensors such as Coolant Temp Sensor.

ECU uses a bunch of sensors to calculate the correct amount of fuel that needs to be injected etc.
 

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2010 B8 A4 Avant 2.0 TDI 120HP
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Discussion Starter · #3 ·
Have you scanned for car for codes? Increased fuel consumption may vary on a couple of things such as MAF, O2 sensors and a bunch of misc sensors such as Coolant Temp Sensor.

ECU uses a bunch of sensors to calculate the correct amount of fuel that needs to be injected etc.
No, I don't have an ODB-II reader. Will definitely get one though, if that will solve this? Thanks anyway for the reply!
 

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No, I don't have an ODB-II reader. Will definitely get one though, if that will solve this? Thanks anyway for the reply!
OBD2 reader does not necessarily solve problems. It allows you to read the cars ECU so you can get a better idea of what the computer is saying and narrow down diagnosing.

Basic scanners allow you to read and erase codes while the next ''level'' you can do data logging etc.
Ross-Tech/VagCom is considered top of the line and you can do a WHOLE bunch of stuff such as coding and enabling/disabling values for your cars ECU (turn on/off Cruise Control in the ECU etc.).

Basic Scan Tool is a must for any Home-DIYer imo
 

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2010 B8 A4 Avant 2.0 TDI 120HP
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Discussion Starter · #5 ·
OBD2 reader does not necessarily solve problems. It allows you to read the cars ECU so you can get a better idea of what the computer is saying and narrow down diagnosing.

Basic scanners allow you to read and erase codes while the next ''level'' you can do data logging etc.
Ross-Tech/VagCom is considered top of the line and you can do a WHOLE bunch of stuff such as coding and enabling/disabling values for your cars ECU (turn on/off Cruise Control in the ECU etc.).

Basic Scan Tool is a must for any Home-DIYer imo
Agree that it is a must-have. I guess I've just not come across a situation where I need one, until now... I feel like the VCDS might be a bit overkill though? Primarily I'd only want diagnostics. I guess it would be fun to be able to have the running lights turn on when you unlock the car at night and such(e.g. "follow-home" lights), if that is a possibility with the VCDS. Otherwise I only need the basic tool so I can know which part to replace, as far as I understand.

I've had the car for almost three years and never deared dip my toes into the world of computer diagnostics etc. when it comes to cars, so forgive my incompetence on the subject matter.
 

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A lot of generic scanners will only read generic OBD codes and can't get into all modules on the car. VCDS can read everything and of course, gets the manufacturer specific codes. You can also use it to do more in depth diagnostics, looking at live data for example. That kind of thing could be useful here - looking at O2 sensor readings, etc. You aren't going to be able to do a lot of customizing things like lights, etc. on a mk4 with it though. That capability is more on the newer cars. OBDeleven is another tool that seems to work well with VWs.
 

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2010 B8 A4 Avant 2.0 TDI 120HP
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Discussion Starter · #8 ·
A lot of generic scanners will only read generic OBD codes and can't get into all modules on the car. VCDS can read everything and of course, gets the manufacturer specific codes. You can also use it to do more in depth diagnostics, looking at live data for example. That kind of thing could be useful here - looking at O2 sensor readings, etc. You aren't going to be able to do a lot of customizing things like lights, etc. on a mk4 with it though. That capability is more on the newer cars. OBDeleven is another tool that seems to work well with VWs.
Seems like VCDS is the solution for me, especially considering the nature of the problem. The only thing that hurts is the price tag (around 350$ over here). Might be easier to just take it to the shop to find out whats wrong. Expensive either way at this point.

Something with fuel mileage complaints I've run into is people's kids or roommates 'borrowing' the car in the middle of the night.
Lol. Neighbour drives a fat jag and I'm 20, but hey who knows. Maybe if I remove the battery the fuel economy will improve?🤔
 

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Discussion Starter · #13 ·
Found a video of a Brit testing OBDeleven on MK4 Golf

Yeah saw that one too. Looks like what I need. He uses android but I think the one I previously linked also supports iPhone, and is a newer version. Thank anyways!
 

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Discussion Starter · #14 ·
Ok so I got the OBDEleven today, and it works as expected.

I got the fault code 00537 - Oxygen Sensor Regulation - lower limit stop value.
Status: intermittent

Link to ross-tech wiki

Could this be my injectors being faulty, since the fuel efficiency is so poor?
Or could this simply be the sensor being faulty? Any recommended course of action, other than what is stated on the wiki?
 
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