Cadillac, Buick and GMC: common OBD-II codes across the GM range

Cadillac, Buick and GMC share engines, transmissions, modules and suppliers with each other and with Chevrolet. A fault pattern documented on one badge almost always applies to the others, which makes the shortlist short.

Companion reading: Chevrolet and GM common OBD DTC codes.

The codes that recur

P0011 and P0014 — variable valve timing

Very common across GM’s Ecotec and V6 range. The usual cause is not the phaser but the oil control solenoid, clogged by sludge from extended oil change intervals.

Old or wrong-grade oil is the root cause more often than a mechanical part. Detail: VVT P0011 and P0014 and engine oil viscosity and approvals.

P0016 — crankshaft and camshaft correlation

Timing chain stretch, and a well-documented issue on several GM four-cylinder engines. A rattle for a second or two on cold start is the early warning, and it is worth acting on before the chain skips a tooth.

Crankshaft-camshaft correlation P0016 and timing chain vs belt DTC codes.

P0300 and cylinder-specific misfires

Coils, plugs and — on direct injection engines — carbon on the intake valves. The swap test separates the first two: P0301 to P0304.

Direct injection deposits are a genuine issue on the Ecotec turbo and V6 DI engines: GDI carbon buildup.

P0171 and P0174 — lean

Intake manifold gaskets and PCV systems. GM plastic intake manifolds and their gaskets are a known source. The fuel trim comparison at idle versus 2500 rpm settles leak versus metering: P0171 and P0174 and P2187 lean at idle.

P0442 and P0455 — EVAP

Purge and vent valves, and canisters that corrode underneath the vehicle. Check the cap, then smoke test rather than replacing parts speculatively: P0442 and P0440 and P0446 valves.

P0420 — catalyst

Common on higher-mileage examples. Rule out an exhaust leak near the downstream sensor and an ageing upstream sensor before quoting a catalyst: P0420 and P0133.

Transmission codes

The 6L and 8L automatics are widely used across the range. Torque converter clutch shudder is the recurring complaint, and it frequently responds to a fluid change with the correct specification if caught early.

P0740 and P0741, transmission shudder at low speed and P0700, which is only a pointer to the real code in the TCM.

Electrical: check voltage before anything

GM vehicles are not unusual here, but the principle bites hard on well-equipped Cadillacs with many modules: a weak battery produces communication codes across several modules that look like several separate failures.

U0100 lost communication with ECM, U0121 lost communication with ABS and when the scanner lies about ghost codes.

Test the battery under load before diagnosing any individual module. This single step resolves a large share of multi-code Cadillac complaints.

Cadillac specifics

Magnetic ride control on performance models is a chassis system outside generic OBD-II, and its dampers are expensive. Symptoms are ride quality rather than codes you can read.

Adaptive cruise and driver assistance require calibration after windscreen or bumper work: ADAS calibration.

GMC and truck specifics

Diesel Duramax models add DPF and emissions hardware with the usual short-trip vulnerability: DPF light on and P2002 and P2463.

Towing is what these vehicles are bought for, and transmission fluid temperature is the reading that matters most on a long tow: transmission overheating warning and towing an automatic.

Four-wheel drive adds a transfer case whose oil is routinely never changed: differential and transfer case care.

If the car was imported

North American specification vehicles brought into other markets carry a few wrinkles: emissions thresholds set against EPA standards rather than local ones, and occasionally different module calibrations.

Generic OBD-II reads identically regardless. See OBD-II vs EOBD vs JOBD, import car, what to check and US salvage import OBD diagnostics.

That last one matters. A significant number of GM vehicles reach other markets through salvage auctions, and a pre-purchase scan plus a careful look at airbag status is not optional — airbag light on causes.

Try it on the free tier of the app — pair an ELM327 adapter and check control module voltage first on any multi-code GM complaint. Low supply manufactures codes across modules, and ruling it out costs nothing.