Car diagnostic fee
Most shops charge for diagnosis, usually about one hour of labor for a check-engine light or a drivability problem, with more time for electrical or intermittent faults. Write the fee on the estimate before you start, say whether it's credited toward the repair if the customer goes ahead, and get the customer's OK. In states with repair laws, diagnosis is work that needs authorization like any other.
Ways to charge
| Method | How it works | Good for |
|---|---|---|
| Flat diagnostic fee | A fixed price, typically one hour of labor | Check-engine lights, no-starts, common complaints |
| Hourly, with a cap | Labor rate × time, not over an amount the customer approved | Electrical, intermittent and network faults |
| Credited if repaired | Fee waived or deducted when the customer approves the repair | Winning the repair job |
A code read isn't a diagnosis
Parts stores read codes for free, so customers sometimes balk at a fee. Explain what they're paying for: the code tells you which system, the diagnosis finds the failed part with tests, so they don't pay for parts they didn't need. Put the findings in the diagnosis field of the repair order so the customer sees the work.
On the estimate
- Customer concern, in their words: "check engine light on, rough idle".
- Line: "Diagnosis, up to 1.0 h" with the price.
- Note whether it's credited toward the repair.
- The customer's authorization, with date and time.
- After diagnosis: a new estimate for the repair and a second authorization.
California requires a written estimate and authorization before any work, including diagnosis and teardown; Florida, Illinois, Ohio and other states have their own thresholds. See auto repair laws by state.
Diagnosis and repair on one ticket. WrenchTicket keeps the concern, diagnosis and each added-work authorization with name, method, date and time. With Pro, the customer approves the repair estimate on their phone from a link. $15 a month.
Write an estimateQuestions
Can a shop charge a diagnostic fee if the customer doesn't fix the car?
Yes, if the customer approved the fee before the work. That's why it goes on the estimate.
Should I waive the fee if they approve the repair?
Many shops do, at least partly. If you do, show the fee and then the credit on the invoice so the customer sees the value.
What if diagnosis takes longer than estimated?
Stop, call the customer and get approval for more time before continuing. Record who approved, when and how.
Checked October 31, 2026. Fees vary by shop and region; state rules are summarized on our state laws page. Not legal advice.