Automotive sensors & DTC codes — a surveyor's diagnostic reference.
Modern cars, trucks, buses, tractors and BS6 commercial vehicles are full of sensors — and every one can set a fault code. This guide maps the major sensors to their job, their failure symptoms and the common OBD trouble codes, with the one caveat that matters most on a claim: a fault code is not proof a sensor has failed. For surveyors documenting electronic and consequential damage after a collision, flood or fire.
In short
- A sensor is a physical component that measures something; a DTC (Diagnostic Trouble Code) is the code the ECU stores when a reading or circuit is out of range.
- A DTC points to a system or circuit, not always a failed sensor — wiring, a connector, supply voltage, an exhaust leak or a mechanical fault can set the same code.
- "Lambda sensor" and "oxygen sensor" usually mean the same sensor family; there are many other sensors and diagnostic systems too.
- After a flood, fire or heavy collision, sensors, the ECU and the wiring harness are among the most vulnerable and expensive items — and often what tips a claim toward total loss.
- On a survey, read the stored codes, note which systems warn, and photograph damaged sensors and connectors — document, don't repair.
Sensor vs DTC — the distinction that trips people up
These two words get used interchangeably on the shop floor, but they are not the same thing, and the difference matters when you write a report:
Sensor (the component)
A physical device that measures a quantity — air flow, manifold pressure, throttle position, coolant temperature, oxygen in the exhaust, wheel speed. It sends a signal to the ECU. You can see it, photograph it, and it can be water- or impact-damaged.
DTC (the code)
A Diagnostic Trouble Code the ECU stores when a signal or circuit falls outside its expected window — e.g. P0102 for a low MAF signal. It names where the problem was seen, not what caused it.
The full sensor & DTC map
This reference chart lays out the major sensors in a modern vehicle, their locations, the common fault codes and basic testing methods — a quick orientation before the detail below.
Sensor categories
It helps to group sensors by the system they serve — this is also how the DigiSurvey reference database is organised:
Engine & air intake
Govern air, fuel metering and ignition timing.
Fuel system
Measure fuel pressure and quantity.
Exhaust & emissions
Control emissions & after-treatment (critical on BS6).
Braking & stability
Feed ABS, ESP and stability control.
Transmission & drivetrain
Manage shifting & driveline.
Body & safety
Occupant safety and convenience.
Tyres & chassis
Monitor tyres and ride height.
EV / Hybrid
Manage the high-voltage system (critical on EVs).
Key sensors — function, symptoms & common DTCs
| Sensor | Function | Typical failure symptoms | Common DTC(s) |
|---|---|---|---|
| MAF (Mass Air Flow) | Measures intake air mass for fuelling | Poor pickup, low power, higher fuel use, check-engine light | P0100–P0104 |
| MAP (Manifold Abs. Pressure) | Measures intake manifold pressure | Rough idle, poor power, black smoke | P0105–P0109 |
| TPS (Throttle Position) | Detects throttle opening | Erratic idle, hesitation, limp mode | P0120–P0124 |
| ECT (Coolant Temp) | Measures engine coolant temperature | Hard start, rich/lean running, fan issues | P0115–P0119 |
| Oxygen / Lambda | Oxygen in exhaust (pre-catalyst) | Poor mileage, high emissions, rough running | P0130–P0167 |
| Crankshaft position (CKP) | Engine speed & position | No-start, stalling | P0335 |
| Camshaft position (CMP) | Camshaft position for timing | Misfire, hard/no start, rough idle | P0340 |
| Catalyst system | Converter efficiency (via O₂ sensors) | High emissions, MIL on | P0420 |
| Vehicle speed (VSS) | Road speed | Speedometer error, shift issues | P0500–P0503 |
| NOx (Diesel, after SCR) | Oxides of nitrogen in exhaust | Limp mode, AdBlue warnings, high emissions | P20xx family |
| EGT (Exhaust Gas Temp) | Exhaust temperature (diesel) | DPF regen faults, derate | P040x / P24xx |
| DPF differential pressure | Soot load across the DPF | Blocked-DPF warning, limp mode | P244x |
| ABS wheel-speed | Each wheel's speed | ABS light, no ABS/ESP | C0035–C0050 |
| Steering-angle | Steering angle for ESP | ESP/traction light, stability loss | C0051 / U-codes |
| Airbag impact | Detects collision for airbag deploy | Airbag warning light | B00xx |
| TPMS | Tyre pressure (& temperature) | TPMS warning, wrong readings | C0750 family |
DTC ranges are indicative; the exact definition of a code can vary by manufacturer and model, and many C- and B- codes are manufacturer-specific. Always confirm the code against the vehicle maker's definition.
Common DTC families — quick reference
| DTC | Sensor / system | What it points to |
|---|---|---|
| P0100–P0104 | MAF | Mass air-flow circuit family |
| P0105–P0109 | MAP | Manifold / barometric-pressure circuit family |
| P0115–P0119 | ECT | Engine coolant-temperature circuit family |
| P0130–P0167 | Oxygen / Lambda | Oxygen-sensor-related code families (exact meaning depends on the code) |
| P0335 | Crankshaft position | CKP sensor circuit |
| P0340 | Camshaft position | CMP sensor circuit |
| P0420 | Catalyst | Catalyst-system efficiency below threshold |
| P0500 | Vehicle speed | Vehicle-speed sensor circuit |
| C0035 | ABS wheel-speed | Commonly left-front wheel-speed circuit; exact definition varies by maker |
Basic testing methods
Visual inspection
The sensor, its connector and wiring — corrosion, water, melt, impact.
OBD scan tool
Read stored DTCs and live data from the ECU.
Multimeter
Voltage, resistance and continuity on the sensor and its circuit.
Oscilloscope
The signal waveform — catches intermittent and shape faults.
Live-data analysis
The sensor's actual reported values against expected ranges.
Physical testing
Air, heat or pressure applied to confirm response, where appropriate.
Why this matters on an insurance survey
A surveyor is not diagnosing the car to repair it — but sensors and the vehicle's electronics are often where the real money, and the total-loss decision, sits after a serious loss:
- Flood / water ingress: sensors, the ECU, the wiring harness and connectors are among the first and costliest casualties. Water in the harness and control modules is frequently what pushes a flood claim toward constructive total loss. Photograph waterlines, wet connectors and corroded sensors; don't re-crank a flooded engine.
- Fire & heat: melted harnesses, heat-damaged sensors and burnt modules — document the spread and the affected systems.
- Collision: front-end impacts take out airbag, radar/parking, O₂, MAF and crank/cam sensors; note deployment and which sensors sit in the crush zone.
- BS6 commercial vehicles: the SCR/DPF/AdBlue after-treatment electronics (NOx, EGT, DPF-pressure, DEF sensors) are expensive and sensitive — list them separately when damaged.
- EV / Hybrid: high-voltage battery, inverter and insulation-monitoring sensors carry both cost and safety implications — treat with caution and note them distinctly.
Reading the stored codes and noting which warning lights are on is useful evidence of consequential electronic damage — but in the report, state what you observed and photographed, and keep the sensor-vs-DTC distinction clear so a code is never written up as a confirmed failed part without inspection.
Frequently asked questions
What is the difference between a sensor and a DTC?
Does a DTC always mean the sensor is faulty?
Why do sensors matter on a survey?
How are sensors tested?
Capture damaged sensors and modules, and build the report around the evidence.
DigiSurvey stamps every photo with GPS and time, lets you tag damaged sensors, modules and harnesses, and carries it into a spot and final report with the estimate and total-loss working — a defensible record of consequential electronic damage.