P0600 during emissions test

Took my 2008 Impreza in for emissions testing today. When I pulled in the check engine light was not on and the car was running fine.

Then they hooked up the diagnostic link & started the car, and the check engine light kicks on with a “P0600 Serial Communication Link Malfunction” code. Whereupon I fail because… the check engine light is on.

3 hours later, now the check engine & ABS lights are off again. What gives? Is there a real problem here & it’s just a coincidence of the ages that it would show up during the emissions test? Or was this somehow triggered by the test, & will happen again next time I head in?


Go back, talk to the manager and explain what happened last time, show that there’s no check light on.
Be polite.
If it happens again have it documented in detail.
You don’t say if in your state there’s inspection stations or just regular shops, but you should be able to take this up a level from the routine inspector.

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Good point, thanks. This is in Colorado, where there is a state-approved testing station under the management of a single company. They gave me a vehicle repair form to be filled out by a technician & brought back for a free re-test.

There have been reports of low battery voltage causing fault P0600 on these vehicles, have the battery tested.

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