CKFCar Known Faults
P0128minor Severity

Coolant Thermostat (Coolant Temp Below Regulating Temp)

The engine is not reaching its optimal operating temperature within the expected timeframe, usually because the thermostat is stuck open.

Common Symptoms

  • Temperature gauge drops when driving at high speeds
  • Heater blows lukewarm air instead of hot
  • Noticeable drop in fuel economy (MPG)

Generic Causes

  • Thermostat stuck in the open position
  • Failing engine coolant temperature (ECT) sensor
  • Low engine coolant level

Known Cars Affected by P0128

We have cross-referenced P0128 against our database of known faults. Below are specific cars where this code frequently appears, along with the detailed diagnostic and repair instructions for that specific vehicle.

Coolant Loss from Cylinder Head

Severe
2012-201860,000–120,000 miles£500–£900

The 1.0 EcoBoost has an integrated exhaust manifold cast into the cylinder head. This design causes head gasket stress and coolant loss, sometimes causing overheating.

Coolant Loss and Head Gasket Failure

Severe
2006-201460,000–120,000 miles£400–£700

The Z12XE and Z12XEP 1.2-litre petrol engine in the Corsa D is known for coolant loss. In many cases this escalates to head gasket failure if not caught early.

EGR Cooler Failure and Soot Ingestion

Severe
2009-201360,000–120,000 miles£400–£800

The 1.6 TDI common-rail engine has a well-documented EGR cooler failure. Coolant can leak into the intake causing rough running or, in severe cases, catastrophic engine failure from hydro-lock.

EGR Cooler and Valve Failure

Moderate
2007-201270,000–130,000 miles£600–£1200

EGR cooler failure on the N47 is common from 70,000 miles. Coolant leaks into the intake manifold and the EGR valve sticks, causing power loss and rough running.

Engine Thermostat Sticking Open

Minor
2004-201160,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Thermostat Housing Leak and Failure

Moderate
2006-201340,000–90,000 miles£200–£350

The plastic thermostat housing on the R56 warps and cracks, causing coolant leaks. The integrated temperature sensor also fails, causing erratic fan behaviour.

Thermostat Failure and Overheating Risk

Moderate
2012-201850,000–100,000 miles£80–£180

The plastic thermostat housing on the 1.0 EcoBoost is prone to cracking. A stuck-open thermostat causes the engine to run cold and burn more fuel; a stuck-closed thermostat causes rapid overheating.

Coolant Loss from Integrated Exhaust Manifold

Severe
2011-201860,000–120,000 miles£500–£900

The 1.0 EcoBoost's unique integrated exhaust manifold/cylinder head design causes head gasket stress. Coolant loss without visible leaks is a known issue on higher-mileage Focus Mk3 examples.

Water Pump Failure (Belt-Driven Internal)

Severe
2011-201880,000–140,000 miles£250–£500

The 1.0 EcoBoost uses a belt-driven water pump. When the pump fails, coolant circulation stops and the engine overheats rapidly. Because it is inside the engine, early detection requires vigilance.

EGR Valve and Cooler Failure

Severe
2011-201860,000–120,000 miles£400–£700

The EGR valve and cooler on the Mk3 Focus 1.6 TDCi are known to fail together. EGR cooler failure can cause coolant to enter the intake — a more serious failure than a simple blocked valve.

Coolant Loss and Head Gasket Failure

Severe
2014-201960,000–120,000 miles£500–£800

The Corsa E 1.4 turbo shares the head gasket vulnerability of its predecessors. Coolant loss without visible external leaks is a red flag that demands immediate investigation.

EGR Cooler Failure and Intake Contamination

Severe
2012-201570,000–130,000 miles£500–£800

EGR cooler failure on the Astra J 1.6 CDTi causes coolant loss and in severe cases, coolant enters the intake manifold. This is a more serious failure than a simple EGR valve block.

Engine Thermostat Sticking Open

Minor
2014-201960,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2010-201560,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2012-201960,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2008-201760,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2005-201160,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2011-201860,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2006-201260,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2012-201660,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2008-201560,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2007-201260,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2012-202060,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2007-201160,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2007-201260,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2013-202160,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2012-201860,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2012-201960,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2012-201760,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2006-201160,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2004-201160,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2015-202160,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2011-201860,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2007-201460,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2010-201560,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2009-201660,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2011-201860,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2012-201860,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2005-201460,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2006-201260,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2006-201260,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2009-201360,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2003-201360,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2012-201760,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2006-201360,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2007-201260,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2012-201560,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2011-201560,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2006-201260,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2006-201460,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2009-201360,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2008-201760,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2008-201260,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2006-201360,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2004-201360,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2013-201760,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2004-200960,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2005-201260,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2007-201960,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2010-201960,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2007-201260,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2004-201060,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2012-201560,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

Engine Thermostat Sticking Open

Minor
2006-201460,000–120,000 miles£100–£250

The engine coolant thermostat fails in the 'open' position. The engine never reaches its optimal operating temperature, killing fuel economy.

EGR Cooler Failure and Coolant Loss

Severe
2008-201570,000–140,000 miles£500–£900

EGR cooler failure is common on the B8 A4 TDI. Internal corrosion allows coolant to leak into the intake — initially causing rough running and white smoke.

EGR Cooler Failure

Severe
2008-201770,000–140,000 miles£600–£1000

EGR cooler failure on the Insignia 2.0 CDTi causes coolant to enter the intake manifold — a serious failure that requires immediate attention.

EGR Cooler Failure and Coolant Loss

Severe
2012-201960,000–130,000 miles£500–£800

EGR cooler failure on the Kuga Mk2 causes coolant to enter the intake. Left unchecked this results in rough running, white smoke and potential engine damage.

EGR Cooler Failure

Severe
2010-201470,000–140,000 miles£500–£900

EGR cooler failure on the Passat B7 2.0 TDI causes coolant loss and white smoke. The internal corrosion of the cooler allows coolant into the intake manifold.

EGR Failure and Coolant Loss

Moderate
2007-201070,000–140,000 miles£700–£1200

EGR cooler failure on the E60 520d N47 causes internal coolant leaks into the intake manifold. Combined with EGR valve carbonising, both components typically need replacing together.

Cooling System Thermostat Housing Failure

Moderate
2007-201070,000–140,000 miles£200–£400

The plastic thermostat housing on the N47 is notorious for cracking and causing coolant loss. BMW used plastic for this component in a bid to save weight — it fails prematurely.

EGR Valve and Cooler Failure

Severe
2014-201970,000–140,000 miles£600–£1100

The Ingenium 2.0 TD4 engine in the Discovery Sport develops EGR valve and cooler failures. The cooler can cause coolant to enter the intake on higher-mileage examples.