Expert: Out-of-spec parts can still be OK
Congressional eyebrows were raised on March 27 when Delphi Automotive told a congressional committee that General Motors had accepted a Delphi ignition component that failed to meet the automaker's specs.
The part in question, a small spring, applied insufficient torque to hold the ignition key in the "on" position if drivers accidentally nudged it with their knees.
Why would an automaker knowingly accept a part that is out of spec?
"Just because a part is out of tolerance doesn't mean that it's the root cause of a failure," said Scott Gray, a senior program manager for quality at the Automotive Industry Action Group, an industry research consortium in suburban Detroit.
But if the out-of-spec part "affects a component's fit, form or function, that's when you are expected to do a full root-cause analysis," Gray said.
Sources contacted for this report were unable to indicate how often automakers use out-of-spec parts, but it happens frequently enough to require a protocol.
Since 1993, the Detroit 3 have had a standard procedure to evaluate out-of-spec parts. To perform that analysis, engineers use two relevant documents: the Failure Mode Effects Analysis and the Production Part Approval Process.
The Failure Mode Effects Analysis can indicate whether an out-of-spec part would work anyway, or whether it might suffer a catastrophic failure. Engineers perform the analysis at the outset of a component's development. It can tell what might go wrong if a part varies from the blueprints.
The Failure Mode Effects Analysis is used to evaluate all components, not just defective parts. But it can help engineers assess the consequences of using an out-of-spec part.
The Failure Mode Effects Analysis, part of an industry standard developed by GM, Ford and Chrysler in 1993, is a living document, Gray said. That is, it is updated and revised as an automaker tests a component, redesigns it or receives field reports of failures.
Once that analysis is completed and the part is designed, the supplier undergoes a Production Part Approval Process, another industry standard developed by the Detroit 3.
A supplier performs a Production Part Approval Process to show that it can properly produce the component. It is serious business; automakers won't pay suppliers for tooling until they successfully complete it.
And if any changes are made -- even seemingly trivial alterations of a component's design or manufacture -- the supplier must update its Production Part Approval Process, said one senior engineer who works for a GM supplier.
The engineer, who asked not to be named, told Automotive News that his company once had to get GM's approval to move some production tooling 10 feet to a new location on the factory floor.
In sum, an automaker can accept out-of-spec parts.
A key document in the current crisis is the Failure Mode Effects Analysis -- that is, the company's failure analysis -- that might indicate whether GM knew in advance that an out-of-spec spring might cause a malfunction.
Company spokesman Greg Martin last week declined to comment. "We look forward to sharing findings, as appropriate, once completed," Martin said. "Until then, we will provide no preliminary comment."
You can reach David Sedgwick at email@example.com.