How To Find Tough Leaks

Find those tough to spot leaks with smoke machines, scan tools, emissions analyzers and more.


In the old days, you used to be able to see or smell that a vehicle was burning antifreeze. In 2012, catalytic converters are too good for that. The Grand Marquis’ bad head gasket was diagnosed with an emissions analyzer. It was the only tool that could have done the job.

Q: What is the best way to diagnose a tough air suspension problem?

A: Typically, vehicles with air suspension have a combination of problems by the time they make it to your shop. It’s not atypical to have a car which has a bad ride height level sensor, two bad air springs, and a bad compressor. Problems tend to come in bunches with these systems, but that’s a discussion for another day.

The best way to begin diagnosing an air suspension problem is with a scan tool. To get the job done you need a factory scan tool or an aftermarket scan tool with factory capabilities.

Here’s a small case study on a real-world problem car: On a 2004 BMW X5 with leaking rear air springs, you throw soapy water on the suspension and do not see any bubbles. So you need to scan for codes to find out where to start your diagnosis. After being told to check the front right ride height level sensor by the tool, you should swap the front sensors to see if it’s a sensor or wiring/module issue. If the code stays on the same sensor, immediately suspect the module. Being that more modules go bad more than wiring, to test this presumption simply swap the signal wires of those sensors to the module and scan the vehicle. As you can see in the screenshots, the ride height values on the front right sensor remain static, even though it is, in fact, directly wired to the front left sensor. With the right scan tool and a little ingenuity, you can diagnose that this vehicle had a bad module. (See Fig. 4 and 5, much thanks to Bernard Tripp of Autohaus for devising this technique).

Another good strategy for tough-to-find leaks is to use a smoke machine and an emissions analyzer (See Fig. 6). You see, you can find a spot where you can insert CO2 into the vehicle and simply use your emissions analyzer to find spots where there are elevated levels of CO2. This will help you spot the leaking air spring or compressor check valve that you cannot find by another means (such as soapy water).

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