Seeing fault codes on a Land Rover scan tool can be frustrating, especially when the code points toward the engine control unit. Two codes that often cause confusion are P2228 and P0666.

At first glance, neither code seems to explain why the vehicle has poor performance, reduced power, warning lights, or intermittent limp mode. However, both faults can affect how the ECU calculates engine load and protects itself from excessive heat.

The important thing is not to replace the ECU immediately. These faults can also be caused by damaged wiring, weak power supplies, poor grounds, moisture, corrosion, or a sensor circuit that is shorted.

Here is what both codes mean and how a professional technician should approach the diagnosis.

P2228 – Barometric Pressure Sensor “A” Circuit Low

The fault code P2228 means the ECU has detected a lower-than-expected electrical signal from the barometric pressure sensor circuit.

The barometric pressure sensor measures atmospheric pressure outside the engine. The ECU uses this information to understand the vehicle’s altitude and the density of the air entering the engine.

Air density changes depending on altitude and weather conditions. At higher elevations, the air is thinner. In cold, high-pressure conditions, the air is denser. The ECU uses the barometric pressure reading to help adjust fuel delivery, ignition timing, turbocharger control, and engine load calculations.

When the signal is too low, the ECU may no longer trust the pressure reading. In many vehicles, the barometric pressure sensor may be a separate component. In others, it can be integrated into another sensor or even located within the engine management system. That is why the correct Land Rover wiring diagram and model-specific service information are essential.

A generic OBD-II definition describes P2228 as a low electrical value in the barometric pressure sensor or its related circuit. (OBD-CODES)

Common causes of P2228

The most likely causes include:

• Damaged wiring near the sensor
• Loose, bent, or corroded connector pins
• Missing or weak five-volt reference voltage
• Poor sensor ground
• Signal wire shorted to ground
• Faulty barometric pressure sensor
• Water contamination near the ECU or connector
• Internal ECU fault
• Previous repair work that damaged the harness

A low code does not always mean the sensor itself is bad. In fact, replacing the sensor without checking the circuit is one of the most common diagnostic mistakes.

Symptoms you may notice

A Land Rover with P2228 may show:

• Check engine light
• Reduced engine power
• Hesitation during acceleration
• Poor throttle response
• Unstable idle
• Increased fuel consumption
• Turbocharger performance problems
• Difficult starting
• Limp-home mode
• Additional air or fuel mixture codes

Some drivers notice the problem more clearly when climbing hills, driving at high altitude, or accelerating under heavy load.

What to check first

Start with a complete vehicle scan rather than looking at P2228 alone. Other stored or pending codes may help identify whether the problem is caused by a shared five-volt supply or ground circuit.

Next, inspect the wiring and connector carefully. Look for:

• Green corrosion on terminals
• Water marks
• Oil contamination
• Chafed insulation
• Broken wires inside the loom
• Pins pushed backward into the connector
• Previous repairs using poor-quality crimp connectors

With the ignition switched on, a technician should verify the sensor’s power supply, ground, and signal circuits. The exact voltage values vary by vehicle and sensor design, so the factory wiring diagram should be used instead of relying on a guessed specification.

A professional diagnostic process generally includes:

1. Confirming the code with a quality scan tool
2. Checking freeze-frame data
3. Comparing barometric pressure with known atmospheric pressure
4. Testing the five-volt reference circuit
5. Testing the sensor ground
6. Checking the signal wire for a short to ground
7. Inspecting ECU connectors
8. Clearing the code and completing a road test

The freeze-frame data can be especially useful. It shows the engine speed, load, temperature, and vehicle conditions present when the fault was stored.

P0666 – Control Module Internal Temperature Sensor “A” Circuit

The code P0666 refers to a problem with the internal temperature sensor circuit inside a control module. Depending on the vehicle, that module may be referred to as the PCM, ECM, or TCM.

In simple terms, the ECU is monitoring its own internal temperature and has detected an electrical problem or an implausible reading.

This does not necessarily mean that the engine is overheating. The sensor is generally monitoring the temperature inside the control module itself. The ECU uses this information to protect its electronics and recognize abnormal heat conditions.

The generic definition of P0666 is associated with the internal temperature sensor circuit of the powertrain, engine, or transmission control module. (OBD-CODES)

Common causes of P0666

Possible causes include:

• ECU internal temperature sensor failure
• ECU overheating
• Moisture inside the ECU housing
• Corrosion on ECU terminals
• Poor battery voltage
• Charging system problems
• Damaged ECU ground
• Wiring or communication faults
• Internal circuit board damage
• Incorrect ECU software or calibration
• Heat damage caused by poor mounting or ventilation

On some Land Rover applications using the MED17.8.31 engine management system, an internal ECU fault may become a serious possibility. However, the ECU should only be condemned after power, ground, voltage stability, connectors, and environmental conditions have been checked.

Symptoms linked with P0666

Drivers may experience:

• Check engine light
• Intermittent no-start condition
• Engine cutting out
• Sudden limp mode
• Reduced performance
• Rough running
• Multiple unrelated fault codes
• Communication errors with the scan tool
• Warning messages across the instrument cluster
• Poor fuel economy

If several modules report communication faults at the same time, do not assume that all those modules have failed. A weak battery, poor ground, water intrusion, or unstable power supply can create a long list of misleading codes.

Why P2228 and P0666 Can Appear Together

When P2228 and P0666 appear together, the fault may be bigger than one individual sensor.

Both codes can involve the ECU, its wiring, or its power and ground circuits. A problem in one area may trigger both codes, particularly if the ECU is receiving unstable voltage or has internal damage.

Possible shared causes include:

• Weak battery
• Alternator overcharging or undercharging
• Poor engine-to-body ground strap
• Water entering the ECU area
• Corroded ECU connector
• Damaged five-volt reference circuit
• Internal ECU circuit failure
• Incorrect software or calibration
• Poor-quality tuning or previous ECU repair

The first step is to check the vehicle battery and charging voltage. Modern Land Rover electronics are sensitive to unstable voltage. A battery that starts the engine successfully can still create problems if its voltage drops too far during cranking.

The technician should also inspect the ECU mounting area. Look for damp carpets, blocked drains, water trails, or signs of condensation. Moisture and electronic control units are a particularly unpleasant combination—rather like inviting rain to a laptop party.

Can You Keep Driving With These Codes?

It depends on the symptoms.

If the vehicle drives normally and the codes are stored without active warning messages, it may be possible to drive a short distance to a repair facility. However, continued driving is not recommended if the vehicle is:

• Entering limp mode
• Losing power in traffic
• Stalling
• Cutting out at speed
• Showing multiple electrical warnings
• Running very rich or very lean
• Overheating
• Failing to restart

A faulty barometric pressure signal can affect engine fueling and boost control. An ECU internal temperature problem may also become worse as the vehicle heats up.

For a workshop or tuner, these codes should be treated as diagnostic priorities rather than simple “clear and return” faults.

Should You Replace the Sensor or ECU?

Do not replace expensive parts based only on the code description.

A fault code identifies the system where the problem was detected. It does not always identify the failed component.

Before replacing the barometric pressure sensor, test:

• Sensor power
• Sensor ground
• Signal voltage
• Continuity to the ECU
• Shorts to ground
• Shorts to battery voltage
• Connector condition

Before replacing or repairing the ECU, test:

• Battery voltage
• Alternator output
• ECU power feeds
• ECU grounds
• Main relays
• Fuse box condition
• Connector pins
• Water intrusion
• Communication network faults

If the wiring and power supplies are correct and P0666 returns immediately, the ECU may require specialist testing, repair, cloning, or replacement. Any replacement ECU may also need programming, immobiliser matching, configuration, and software calibration.

A Practical Diagnostic Order

For the best results, follow this order:

1. Perform a full scan

Record all stored, pending, and manufacturer-specific codes. Do not erase anything before saving the data.

2. Check the battery and charging system

Low voltage can create faults that look like sensor or ECU failures.

3. Inspect the ECU area

Check for moisture, corrosion, heat damage, and damaged connectors.

4. Test grounds and power supplies

Voltage-drop testing is often more useful than a basic continuity check.

5. Diagnose P2228

Verify the barometric pressure circuit, sensor supply, ground, signal, and wiring back to the ECU.

6. Diagnose P0666

Check whether the code returns immediately after clearing. If it does, inspect ECU power, grounds, temperature conditions, and internal module health.

7. Check software and tuning history

Modified software, incorrect calibrations, or an ECU that has been previously repaired may affect diagnosis.

8. Clear the codes and road test

After repairs, the vehicle should be tested under different conditions, including cold start, warm operation, idle, acceleration, and load.