GUIDE / OBD-II
Does an older bulletin still apply?
An old publication can still apply to an old vehicle. Its date alone does not prove obsolescence. Check explicit replacement notices, model, engine, production range, symptoms and software. A bulletin is not automatically a recall or a promise of free repair. This index uses US NHTSA manufacturer communications; absence here does not rule out documents for another market.
Before replacing a part
Record codes and freeze-frame data. Check battery condition, related codes and visible wiring or hose damage. Follow the vehicle's diagnostic procedure and test results before replacing parts.
Scan worksheet →Source-backed code explanations
Sources and interpretation
Read the meaning first, then follow the cited manufacturer pages. The explanations and vehicle-specific examples have different scopes; verify the exact application before using a repair instruction.
- Manufacturer Communications — Overview and Access to Publicly Available Manufacturer Communications ↗
National Highway Traffic Safety Administration
Defines the US manufacturer-communications collection, including service notices, warranty/policy extensions and both safety-related and non-safety defects; explains public publication. Presence in this collection alone is not evidence of a recall, warranty entitlement or worldwide applicability.
- 21-NA-146 — MIL Illuminated, DTC P0011 and/or P0014 Set — June 2021 ↗
General Motors · PDF 1, 2, 3
Applicability/version example only: 2019 Chevrolet Silverado 1500 and GMC Sierra 1500 New Model with L3B 2.7L, specified regions. Replaces PIP5648; instructions differ by production date and warn against assuming vehicle applicability. This archived version is not asserted to be the latest service instruction.