O2 sensor, catalytic converter, EVAP leak, MAF sensor, ignition coil, or fuel trim faults.

• ⚡ Rough idle, stalling, poor acceleration, fuel smell
• 📈 Increased consumption, failed emissions test

• OBD2 scanner: record all codes (P0011, P0300, P0420, etc.)
• Live data: fuel trims > ±15% indicates vacuum leak / injector issue.
• Smoke test: pressurize intake/evap system to find hidden leaks.
• Power balance test: identify misfiring cylinder.
• Oscilloscope: check crank/cam sensor signals (advanced).

diagnostic £45–95 O2 sensor £190–330 ignition coil £140–250 catalytic converter £800–1800 MAF sensor £210–400

Alternator failure, voltage regulator, broken belt, corroded terminals.

• 🚘 Dim lights, slow crank, dashboard flicker, “click” when starting.

• Multimeter: engine off 12.4V+; engine running 13.8–14.8V (if not, alternator).
• Load test: carbon pile tester on battery (CCA).
• Check belt tension & condition.
• Parasitic draw test (if battery drains overnight).

battery 70–190£ alternator 340–850£ belt+ tensioner 120–220£

Low oil level, worn pump, clogged pickup, or wrong viscosity.

• 🔊 Ticking lifters, overheating, light flickers at idle.

• Dipstick check: level and condition (milky? sludge?).
• Manual pressure gauge: install in place of sender (min 10psi/1000rpm).
• Inspect oil filter & pressure relief valve.

oil change £50–100 oil pump £700–1400 sender switch £70–130

Wheel speed sensor, tone ring, ABS pump, or low fluid (if red brake light also on).

• 🛑 ABS inactive, traction control light, pulsating pedal, longer stopping.

• Scan ABS codes (C0035, C0040, C1010, etc).
• Check reluctor ring for cracks/missing teeth.
• Measure sensor resistance (800–2000Ω) and AC voltage while spinning wheel.
• Inspect brake fluid level and for leaks.

speed sensor £120–270 ABS module £700–1400 fluid flush £75

Low tyre pressure, sensor battery dead, sensor damaged, relearn needed.

• ⚠️ Light on solid or flashing (fault).

• Check all pressures with gauge (incl. spare if monitored).
• TPMS tool to wake up sensors and read IDs.
• Visual inspect valve stems for damage.
• Relearn procedure after rotation.

sensor £60–150 ea relearn £50–100 valve kit £20

Clock spring, seat belt pretensioner, side impact sensor, or corroded under-seat connector.

• 💺 Light stays on, airbag may not deploy.

• SRS scanner read B codes (B0020, B0030, etc).
• Check yellow connectors under seats – disconnect battery before touching.
• Multimeter test on clock spring continuity.
• Inspect wiring for damage.

clock spring £190–380 seat sensor £150–290 module reset £120–200

EPS motor, torque sensor, low voltage, or fluid level (hydraulic).

• 🔄 Heavy steering, intermittent assist, warning light.

• Check fluid level (if hydraulic).
• Scan EPS module for DTCs (C1604, C1606).
• Check battery voltage – low voltage reduces assist.
• Torque sensor calibration with dealer tool.

EPS motor £950–1750 torque sensor £400–700 fluid flush £90

Low coolant, stuck thermostat, fan failure, water pump leak, head gasket.

• 🌡️ Gauge red, steam, coolant smell, loss of power.

• Check coolant level (when cold).
• Pressure test system for leaks.
• Verify fan operation (AC on, fan should run).
• Thermostat test in hot water.
• Exhaust gas sniffer in coolant for head gasket.

thermostat £150–280 water pump £350–650 radiator £450–900

DPF clogged, failed pressure sensor, ash accumulation, short trips.

• 💨 Reduced power, limp mode, “DPF full” warning, auto cleaning inactive.

• OBD2 check codes (P2002, P242F).
• Read differential pressure sensor at idle vs rev.
• Check ash load with diagnostic tool.
• Forced regeneration with dealer scanner.

forced regen £100–180 pressure sensor £120–220 DPF replacement £1400–2500

Low fluid, quality sensor, pump failure, NOx sensor, crystallization.

• 🧪 Countdown warning, eventually no start.

• Check fluid level and top up with correct AdBlue.
• Scan for reductant system codes (P20EE, P204F).
• Inspect AdBlue injector for blockage.
• Test NOx sensors with multimeter.

AdBlue top up £15–40 NOx sensor £300–550 pump £600–1100

Low fluid, valve body, speed sensor, belt slip, overheating.

• ⚙️ Slipping, harsh engagement, whining noise, limp mode.

• Check CVT fluid level & smell (burnt? low?).
• Scan TCM codes (P17F0, P0868).
• Pressure test line pressure.
• Inspect wiring to transmission.

CVT fluid change £180–300 valve body £800–1500 speed sensor £200–350

One or more glow plugs failed, relay, or controller.

• ❄️ Hard cold start, excessive smoke, rough idle until warm.

• Resistance test each plug (0.5–2Ω).
• Check voltage at plug during preheat.
• Scan codes (P0671–P0674).

glow plug set £80–200 relay £70–140 labour £80–150

Camera blocked, radar misalignment, sensor failure.

• 🚧 Warning lights for lane keep, forward collision unavailable.

• Clean windshield behind mirror.
• Check for DTCs in ADAS module.
• Calibration required after windscreen replacement.
• Inspect radar sensor (front bumper).

camera recalibration £200–400 radar sensor £800–1500

Rear coupling, transfer case actuator, diff oil temp, ABS interference.

• 🛞 Light flashes, system switches to 2WD, binding.

• Check differential fluid.
• Scan AWD control module (C1703, C1704).
• Test rear coupling solenoid resistance.
• Inspect wiring under vehicle.

rear coupling £1100–2100 speed sensor £150–270 fluid change £120