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Heading Off Comebacks And Other Tales

Don’t let that Check Engine light make you look bad.
Thursday, August 28, 2014 - 07:00
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I have a few stories from the shop to share with you this month. The first shares a lesson on not getting caught with your pants down, the other is a tale of a BMW clutch gone sour, and the third? Well, the third is just for your enjoyment! Let’s get to it.

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A Leaking Lincoln
A new customer shows up at our door with a 2002 Lincoln LS (3.0 liter) complaining of a drivability issue and an illuminated Malfunction Indicator Lamp (MIL). Connecting our shop scan tool in Global OBDII mode found System Lean codes (P0171, P0174) for both banks stored in the Engine Control Module’s (ECM’s) memory. But when I check for codes and related data, I don’t stop after checking the initial basics. Look closely at the screen capture in Figure 1. Do you see what I saw?

If you noticed the red warning that not all of the monitors had run since the last time the codes were cleared, you did see what I saw! In fact, to avoid being burned by a comeback I didn’t cause, I make a habit of checking the monitor status on every car we service.

Why? Because the MIL light might return after my repairs and after the missing monitors run. Always remember that some codes, when set by the ECM, might cause testing in other systems to suspend until they have been corrected. As a tech, you perform flawlessly and repair the original cause only to have your customer come back a day, a week or even a month later with the MIL back on. And all they know is they already paid you to turn that irritating light off once already. They don’t want to hear, after the fact, that ii is caused by a whole ne problem. Learn the lesson I learned: If the monitors aren’t all done when you get the car, advise your customer then and there that another problem might be hiding behind the one they came in with.

A quick look at Freeze Frame data and check of fuel trims at idle and at 2,500 rpm told me I was looking most likely for a vacuum leak as the cause of the System Lean codes. The fastest way to find out where the leak is, is to smoke the intake system, and our smoke test pinpointed the leak to a failed PCV elbow. Not uncommon for these engines especially when they have some mileage on them.  The repair went without a hitch and I cleared the codes and took the car for a test drive.

Upon my return, I rechecked the monitor status and looked for pending codes (or first time failures that won’t turn on the light until the second failure). Sure enough, all but the EVAP monitor was complete and a new code was waiting its turn to frustrate its owner, a P0420 Catalyst Efficiency Below Threshold.
Good thing I had this all documented ahead of time!

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