Finding an air suspension leak using diagnostic computer

[Barry]

Most of you know that I’m not really doing much mechanic work now but I still like to keep a finger in (fnarrr) and do bits and pieces. I’ll try to post more stuff like this when I’m doing car work but it won’t be a regular feature. 

This is the easy way to find a leak in an air suspension system without getting your hands dirty. 

The first thing you need is some diagnostic software and a bit of basic knowledge how to use it outside of just scanning and clearing DTCs. This method should be possible with all modern diagnostic software excluding cheap code readers etc. 

You need to enter the suspension system, read the codes and make a note of them then clear them. Clearing them can temporarily enable a disabled system allowing you to carry out tests if you work fast. 

The codes I got were,

01583-Leak detected in system

01577-Switch off due to excessive temperature

 

01583 is pretty self explanatory, it means the system has detected that the air pressure is dropping somewhere, ie an air leak. 

01577 is a symptom of the air leak. It’s important to remember that not every fault code is the main fault, it can be caused by something else which is where a lot of people go wrong. Because of the air leak, the compressor is running for an extended period of time, causing it to overheat and switch off. This could be misinterpreted as a faulty compressor or relay but we will carry out the full diagnostic process rather than fire the parts cannon. FIFT- Fix It First Time

Now we’re going to find out where the leak is. 

Enter the live data function and select compressor relay status and absolute height of all 4 shock absorbers. I have only selected the front shock absorbers because I already know the fault is in the front and am showing for demonstration purposes. 

Now, select graph mode and overlay all parameters in one sheet. 

It should look like this,

You can see from the legend that the dark blue line is compressor on/off status, purple is left front height and light blue is right front height. Unless you are sure the problem is in the front, you should also have selected height for both rear shock absorbers and will have 2 extra lines. 

Notice how when the compressor is in the on state, both shock absorbers raise but the front right never reaches the same level as the left. When the compressor switches off, both shock absorbers start to drop. The front left drops slightly and levels off. The front right drops massively and continues to drop until it reaches the lower limit. The compressor switches on again just before 120s and the cycle begins again.

We can see from this that the problem lies in the front right corner so 75% of the manual diagnostic work has been eliminated. I already know the problem is a leaking airbag because the one on the other side has already been replaced, but you will want to get a spray bottle filled with soapy water and start spraying it all around the air suspension components on the front right corner when the system is running. Wherever you see bubbles, that’s where you have an air leak. This is easier to do if you have a 4 post lift where you can raise the car but still have the wheels grounded. I’m lying on the ground on a piece of carpet which makes it more difficult to access and see components. 

A couple of final warnings. 

Never jack up a car with air suspension without first putting it in jacking mode. This can play havoc with the calibration settings and cause you problems when set the car back down.

Never open any part of the suspension system without first venting the system. Your computer should have a function to do this somewhere in actuations or special functions. The danger of something pressurized flying off and hitting you is real. Slackening a pipe to let the pressure out of the system isn’t a good thing to do. When you loosen a nut on a pipe, you have less threads holding it in place. The pressure can easily overcome the lesser amount of threads, strip them and blow the fitting off. If it doesn’t hit you between the eyes, you’re left with 2 damaged threads which will be difficult to repair. Even if it does hit you between the eyes, you still have to repair the damaged threads you caused after you go to the hospital to get stitches.

One last thing before anyone says it, I know you can use your eyes to find the problem. This is just an exercise in some of the things you can do with your computer.

[Gaurav]

Wonderfully explained with a lot of patience @Barry, here a majority of the mechanic either work with their gut feeling or with overconfidence without relying on the Diagnostic tool lying and eating dust on their workbench.

I have encountered the similar scenario when two mechanic challenged each other for my Pajero slight missing and doof doof noise is due to some adjustment/tune-up and wasted my 4 hours. Later on, one newbie mechanic walks in and ask those two experts that what fault code you found in DTC system and they have realized that they should have checked the DTC codes first. After the full diagnosis, they haven't found any fault code as the actual issue was a mechanical issue of slightly bent valves, which later on you fixed it in 2016.

So moral of the story is relying on science and automation is always helpful, than shooting in dark.

[Barry]

You hit the nail on the head there with newbies versus oldies. I love working with old school guys. You can pick up a lot of neat little tricks that they have learned in 30-40 years of working on cars. On the other hand, many of them are stuck in their comfort zones and refuse to accept that things have moved on or there may be new ways of doing things. I see this a lot in UAE in mechanics young and old. It’s a completely different mindset here and there’s a lot of pride on the line. A lot of mechanics think they know everything and can never admit to being wrong. If you show them, they are likely to tell you that you’re wrong or you don’t know anything. Ok habibi, just trying to help, you spend 4 hours with a test light instead of just plugging the computer in and finding the fault in 10 minutes. I started the process backwards learning on newer cars with ECUs so it comes naturally to me now. Then I got into classic cars. The first time I saw a set of points I was like what the heck is this? An old guy showed me how to set them up. I got it wrong the first time and the car wouldn’t start so I asked for help. The old guy told me I was stupid and fixed it in under a minute with a screwdriver. Next day a Mercedes with a common rail Diesel engine came in, one of the injectors were jammed open. He asked me to check it on the computer because he didn’t know how. I held back on asking him who’s stupid now but we were in different eras of the same boat.

One thing that makes a good mechanic is constant studying. The internet is easily available for most people. Read, read, read, watch YouTube videos, join forums, there is always something to learn about some new technology coming out. The person who believes in his mind that he knows everything and will never need to read will never be a good mechanic. Sure, he’ll be ok for a couple of years until the next technology comes out, then he’ll just say cars are too complicated now, too many computers and send it to someone like me. An open mind is the most important tool any mechanic can own, way more important than a $1,500 snap on digital torque wrench bought on finance. 

[treks]

Speaking of young mechanics who think they know it all - I had one about three years ago who erased all the programming from the ECU on a new BMW, instead of erasing some ghost codes like he thought he was doing. 

And worse, all because he thought he was clever and thought he knew everything about using a diagnostic computer- even though he had no reason under the sun to go anywhere near the car that was in the shop to have a flat tire fixed. Pity the law prevented me from docking his pay for what it cost me to have the car reprogrammed at the dealership. I did fire him though...  

[Barry]

31 minutes ago, treks said:

Speaking of young mechanics who think they know it all - I had one about three years ago who erased all the programming from the ECU on a new BMW, instead of erasing some ghost codes like he thought he was doing. 

And worse, all because he thought he was clever and thought he knew everything about using a diagnostic computer- even though he had no reason under the sun to go anywhere near the car that was in the shop to have a flat tire fixed. Pity the law prevented me from docking his pay for what it cost me to have the car reprogrammed at the dealership. I did fire him though...  

How does that even happen? I like to play around and experiment with things as learning but I’ve never wiped an ECU! I didn’t even know it was possible! Maybe he was trying to do a reflash?

[desertdude]

On ‎10‎/‎2‎/‎2018 at 5:38 PM, Barry said:

Most of you know that I’m not really doing much mechanic work now but I still like to keep a finger in (fnarrr) and do bits and pieces. I’ll try to post more stuff like this when I’m doing car work but it won’t be a regular feature. .....

EDITED FOR SPACE  

OR a guide to make an easy diagnostic overly complicated. If the front right corner is dropping its obvious the problem lie on that end and get straight to the soapy water bottle test. 

[Barry]

Read my disclaimer, last paragraph. 

I have already acknowledged your point. This article is just a basic lesson in some things you can do with your computer. For fun and nothing else. 

Next thing I plan to show is relative compression testing using graph overlays if you don’t have a compression tester gauge. I’m just waiting for a suitable car. 

There are so many things you can do with a diagnostic computer and if you’re a bit nerdy like me, there’s a lot of fun to be had. When the fun is gone from working on cars then what’s left? Sure as hell in UAE the salary isnt the motivation for doing it 

[desertdude]

Well I would say a wrong demo then, whole point of computer diagnostics is to make life easier, not more difficult. This was the opposite. 

Should have started with a compression test first demo first. 

Or here is an idea majority of people here dont have deep digging scan tools, lucky to find avg joe members with even a simple obd scanner even though nowadays its less than 50dhs. Let alone car specific diagnostic tools.

So something how to sort out something using basic OBD.

And I know what you mean. I would spend hours messing with my Range Rover when I first got my JLR scanner. Now I'm bored and just plug it in every now and then just to see if everything is in order

 

[Gaurav]

12 hours ago, desertdude said:

Well I would say a wrong demo then, whole point of computer diagnostics is to make life easier, not more difficult. This was the opposite. 

2

Not actually, as Barry mentioned he wants to show "HOW TO DO IT" with tech means he is teaching people to drive a car - now it's up to you to drive on road or straight off the cliff. 

Secondly, I would still go with computer diagnostic first no matter my eyes and experience says to do soap water test first, just to get things in proper order than shooting in dark. With little tech in place, you can be 100% sure than relying on eyes and experience and waste 4 hours - as I mentioned above. As this OBD II Diagnostic wouldn't take more than 10 mins to run the test and plot the details.

[stig]

10 hours ago, Gaurav said:

Secondly, I would still go with computer diagnostic first no matter my eyes and experience says to do soap water test first,

Occasionally, sensors fail or misinterpret data.
I'm not saying there's a right or wrong way. There are many ways to do it and using on-board diagnostics is one and just helps confirm diagnosis without much physical effort.