The transmission finally quiets down and something worse takes over — a brake vacuum pump that can break the camshaft on its way out.

A second engine thread, smaller but severe. One owner reports "catastrophic engine failure of a 2021 Colorado 3.6L V6" that began with a misfire on a congested street and ended with GM replacing the engine. Another describes complete engine failure attributed to a defective crankshaft, with the truck sitting at a dealer unanswered for 24 days. A third was quoted $6,500 before tax simply to diagnose an engine that started shaking and threw engine, electrical and stability warnings at once. And a fourth reports code P0014 with oil pushed through the bank 1 camshaft solenoid actuator, replaced, then the light returning. None of these has a recall or a Colorado-specific programme behind it. Have a compression and oil-condition check done on any V6 you are serious about.

A cluster with a specific location. Owners report a coolant leak from the hoses running to the thermostat housing with no accident and no visible hose damage — one adding that it has been "commonly reported amongst the same vehicles across the country." Another reports the coolant temperature gauge stuck at around 160 degrees with the cooling fans at high speed constantly, because the thermostat is stuck open, on a truck with under 100,000 miles. Neither is expensive on its own; both are cheap to spot. Look for dried coolant crust around the thermostat housing, check the gauge reaches normal operating temperature on the drive, and listen for the fans after shutdown.

The year's one federal safety recall, and it is a straightforward one. Incorrect bolts may have been used at one or more of the locations that secure the seat belts to the vehicle. If an incorrect bolt was used, NHTSA says the belt may not be properly attached, so it may not restrain an occupant in a crash. Dealers replace the suspect bolts free. The campaign spans a long list of 2021 GM vehicles including the Colorado. Confirm it shows completed by VIN.

Diesel-specific and worth money. GM has a Special Coverage on 2021 trucks with the 2.8-litre diesel (engine code LWN) for a throttle body motor that intermittently fails to complete its position learn cycle in the allowed time. When it happens the check-engine light comes on, a code sets, and — the part that matters — GM says the engine may also be placed in a reduced power mode. Dealers replace the throttle body as necessary and GM's wording is that the repairs will be made at no charge to the customer. Separately, a voluntary emissions recall in the same year reprogrammes the engine computer, which may not have been programmed with all its necessary diagnostic features. Note that an emissions recall is not a safety recall and will not show up alongside 20V811. The wider picture for this engine across these years is a long run of diesel exhaust fluid and particulate filter service work — contamination, pump priming, regeneration diagnostics — rather than bottom-end trouble. The diesel also runs a six-speed automatic, not the eight-speed, so none of the shudder story applies to it.

One owner reports the rear differential failing prematurely at 70,000 miles with loud whining and grinding noises, vibration, and what he calls unsafe driving conditions. GM's own service literature for these trucks includes a rear axle c-clip replacement procedure for a rear axle clunk, and — separately and more tellingly — an engineering bulletin asking technicians in the field to report back on a loud bang or grinding noise from the rear axle area. That is the manufacturer collecting data on a problem rather than fixing it. Drive on a quiet road, on and off the throttle, listening at the rear.

GM's Customer Satisfaction Program for a front differential housing built with a 12 mm hole in its top surface covers 2015 through 2022, so this year is in scope: if the hole is present, the dealer rebuilds the front axle with the correct housing at no charge. Given the rear-axle noise reports above, it is worth having a dealer check both ends by VIN before assuming any noise from underneath is a paid repair.

The generation-long nuisance is here too, and early. One owner reports it at 27,000 miles: the key does not release in park, and the fix is repeatedly adjusting the steering wheel and gear shift until it lets go. The usual repair is a shifter assembly, and owners on adjacent years note it is not covered by the powertrain warranty and can recur after replacement. Cycle park-off-key-out several times before you buy.