Across
1. Camshaft protrusions
4. Structure on cop-car front, sometimes (4,3)
8. Windshield post (1,6)
9. See 6-Down clue
10. Coin substitute at tool booth
11. Unwanted car-radio noise
13. Accelerates, in other words (5,2,3,3)
16. Car-appraisal criteria, ____ wear and tear
18. An intersection accident, slangily (1,4)
21. Fiat 500’s name in Pixar’s "Cars"
22. Dramatic tire failure
23. Planetary gearset’s central element (3,4)
24. Car’s detailed design description, briefly

Down
1. Battery-diagnosis procedure (4,4)
2. A GM brand
3. Vanes in driveshaft’s sliding section
4. Items on car-repair invoice (5,3,5)
5. ’86-’98 Toyota sports hatchback
6. With 9-Across, crankshaft-journal support
7. Piston adjunct
12. Carcinogen in older brake linings
14. Term for valve-seat deterioration
15. Deuce coupes and other customs (3,4)
17. Home of "Vacationland" license plates
19. Emissions-affected atmospheric layer
20. Defunct GM brand, briefly