MINI Countryman Thermostat Replacement in Kirkland, WA: Stuck-Open Thermostat, Damaged Sensor Pins and a Low Coolant Warning

A 2015 MINI Countryman S ALL4 came into our Kirkland shop at 102,983 miles with a low coolant warning and the check engine light on. It left on October 5 with a new thermostat and temperature sensor, a repaired sensor connector, a new coolant hose, a better oil filter than the one it arrived with, and fresh brake fluid.

What the scan tool found

The first step was a full fault scan. The engine computer (the DME) had four codes stored:

The fault scan: two oil pressure codes, and two codes for the coolant temperature sensor (signal stuck low, and a short to ground).

• 33FE: Engine oil pressure control, plausibility: pressure too low

• 3408: Engine oil pressure control valve jams in fully energized position (minimum oil pressure)

• 2947: Coolant temperature sensor signal permanently stuck at low

• 2936: Coolant temperature sensor electrical fault, short circuit to ground

Two systems, two problems. We started with the oil.

The oil filter

With oil pressure codes on the board, our technician pulled the oil filter and drained the oil. The oil had been changed recently, but not by us. What the technician found, in the record’s words: a “cheap aftermarket oil filter installed and oil level slightly low.”

We replaced it with a Mann filter, a quality brand for this engine, and refilled the oil to the correct level. The record doesn’t tie the filter directly to the oil pressure codes, so we won’t either. It’s the kind of thing worth ruling out first on an engine that’s sensitive to oil quality and level.

The thermostat was stuck open

Next came a road test with the coolant temperature on the scan tool. The engine never reached operating temperature. The thermostat was stuck open.

This engine uses a “map” thermostat, one the engine computer can open electronically, built into a housing that carries the coolant temperature sensor. Getting to it meant draining the cooling system and removing the coolant expansion tank, the intake piping and the parts around them.

We removed the housing, cleaned the gasket surface, and installed a new thermostat assembly with a new temperature sensor.

The sensor pins were damaged

That’s when the second electrical problem showed up. The pins in the connector for the coolant temperature sensor were damaged. Those pins are the link between the sensor and the engine computer, so a new sensor alone wouldn’t have reported correctly.

We sourced the proper replacement pins and repinned the connector instead of replacing the harness.

The leaking hose

The low coolant warning had its own cause. The hose to the coolant expansion tank was leaking.

The expansion tank hose, with a trail of coolant running down from the connection. This hose was replaced.

We replaced the hose, topped up and bled the cooling system with long-life premix coolant, and then did multiple follow-up test drives. From the record: no faults returned for the cooling system.

The work performed

Diagnosis and cooling system repair: $1,450–$1,900. Full fault scan, oil filter and oil level correction, road test with live data, new map thermostat assembly with temperature sensor and genuine MINI housing bolts, connector repinned, expansion tank hose replaced, system bled, and repeat test drives. Recorded labor on this line: 4 hours. Cooling system repair and engine diagnostics.

Brake fluid flush: $175–$240. The inspection flagged the brake fluid, so it was flushed from the master cylinder, calipers and lines with new DOT 4 and bled. Road test OK. Brake fluid flush.

What the inspection flagged, but we didn’t fix

• The valve cover was leaking oil. We quoted a replacement valve cover in the $1,100–$1,475 range. The owner held off on it for this visit.

• One brake light was out.

• The tires didn’t match front to rear. Worth knowing on an all-wheel-drive car.

Oil at the edge of the valve cover. Quoted, not done on this visit.

The brakes were healthy at 8 mm front and 5 to 6 mm rear, and the battery tested good.

What it cost

The visit landed in the $1,600–$2,150 range, completed October 2026. Most of it was the diagnosis and cooling repair line, where the thermostat assembly was the largest part and labor made up the rest. The brake fluid flush was the small remainder.

That range reflects a completed historical project, not a current quote. A different car with the same warning light could be a simple hose, or a lot more.

Questions about this job

What does a stuck-open thermostat do?

It lets coolant flow through the radiator all the time, so the engine never warms up to the temperature it’s designed to run at. On this MINI, the road test showed the engine never reaching operating temperature.

Why repin the connector instead of just replacing the sensor?

The new sensor came with the thermostat. The damage was in the connector pins on the car’s side, and a new sensor plugged into damaged pins would still give the engine computer a bad signal.

Does it matter what oil filter goes on a MINI?

We replaced the one we found because it was a low-quality aftermarket filter on an engine with oil pressure codes. We use quality filters on every oil service. More on our oil change service.

Do you work on MINIs?

Yes. MINI is built by BMW, and Totem Lake Auto Care is owned and operated by a BMW master mechanic. More on our MINI repair in Kirkland.

Prepared from our job records for this vehicle: the repair order and technician notes, the diagnostic scan, the multi-point inspection with photos, the parts list and the final invoice.