THE PATIENT
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You don't feel well. You're sitting in the exam room waiting to see your family doctor. After exchanging pleasantries, the
doctor opens his exam with the classic question, "How are you feeling today?" Next, he (or his nurse) performs a few basic
checks on your "systems": He takes your temperature and blood pressure, listens to your heart and breathing, and looks in
your mouth, nose and throat, all to get a basic diagnostic direction.
After considering your symptoms and this basic information, he may order more specific system tests to narrow down your possible
ailments before finally making his conclusion and prescribing the cure. When that's all done, he sends you to the receptionist
to schedule a follow-up appointment to make sure the cure worked.
Sound Familiar?
We essentially follow the same procedure when diagnosing our customer's complaints. We interview the customer and the car
to find out how it's feeling; we perform basic tests on the systems and gather preliminary information before moving on to
more specific tests that help us narrow down the cause of the complaint. Then we reach our conclusion, make our repair, and
verify the result. The only difference, as one physician once told me, is that we can turn our machines off while we work on them — his have
to stay running!
The Jaguar in my bay provides a great opportunity to follow this diagnostic procedure and reinforce the importance of taking
a logical approach to any automotive repair.
Gathering the Basics
FREEZE FRAME DATA FOR CODE
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The first step in any diagnostic procedure should be observation. This step gathers the basic information you need to get
diagnostic direction. It includes interviewing your customer and learning as much as you can about his current complaint.
How does the car drive now? When did the problem start? Has it ever happened before, and if so, what was done about it? The
questions you ask the customer will depend on the nature of the complaint, but the more you know up front, the easier time
you'll have finding the problem.
In the case of the Jag, all the customer could tell me was the Malfunction Indicator Light (MIL) was on. He didn't experience
any change in performance or driveability.
So now it's time to interview the car and see what it can tell me. My first step is to take a look at the car. What is its
overall condition? How many miles are on it? Are there any modifications that may affect the performance of the car or impact
the complaint? Do I have access to any history on the car? (Previous repairs, maintenance history, etc.)
Looking in our history log, I found an entry where the customer had just been in a few weeks ago with an MIL complaint with
codes P0171 (System lean, bank 1) and P0174 (System lean, bank 2). The previous tech had replaced the Positive Crankcase Ventilation
(PCV) hose from the valve to the throttle body because the rubber elbow that attached the plastic hose to the valve had deteriorated
and split. The car itself was in good condition, with no obvious defects seen in the visual inspection.
