TPMS via OBD-II: why the "yellow circle" turned on and how to diagnose tire-pressure sensors

The TPMS light (“yellow horseshoe with exclamation”) seems like “just pump the tires”. Actually on most cars from 2014 onward there are tire pressure sensors with a battery that lasts 5-8 years. If it’s dead, pumping doesn’t help. Below: how OBD-II sees TPMS and what to do about it.

Two TPMS types

Direct TPMS — with sensors inside each wheel

• Every wheel has its own pressure sensor inside the tire (RF transmitter 433 MHz or 315 MHz)
• Transmits pressure + temperature every 30-60 sec to the body ECU
• Internal battery — CR1632/CR2032 lithium, 5-8 year life
• Per-sensor cost: $30-120 (VW OEM — $100+, aftermarket — $30)
• Mandatory replacement when changing tires (valve is fused to the sensor)

Indirect TPMS — via ABS

• No dedicated sensors — uses ABS wheel-speed sensors
• An under-inflated wheel has smaller diameter → spins faster → ABS spots the mismatch
• Cheaper (no dedicated sensors) but doesn’t show which wheel and doesn’t work at standstill
• Requires calibration after wheel/pressure changes (via menu + button)

Key TPMS OBD-II codes

Code	Meaning
C0750	Lost signal from left front sensor
C0755	Right front
C0760	Left rear
C0765	Right rear
C2126	TPMS module fault
C2318	TPMS sensor battery low (may warn 3-6 months before full drain)

What OBD-II can show

Via Mode 22 UDS (manufacturer PIDs):

• Pressure per wheel (kPa or psi) in real time
• Temperature per wheel (°C)
• Sensor battery voltage (measured rarely — once every few days)
• Signal strength — RF signal level per sensor
• Sensor ID (unique ID per sensor — 8 hex chars)

Car Diagnostics supports these parameters for most cars from 2014.

Classic fault patterns

Sensor dead (battery flat)

• Symptoms: TPMS light on and doesn’t clear after inflation; at winter tire swap the shop reports one wheel “not detected”
• OBD: C075X + Signal strength = 0 from one wheel
• Fix: sensor replacement ($30-120)

Signal loss after seasonal wheel change

• Symptoms: first summer/winter after buying the car — TPMS light
• Cause: second wheel set (summer/winter) has its own sensors or none
• Fix: re-learn new sensor IDs via service tool ($20-40 per operation), or install the sensors from the previous set

Mismatch between wheels

• OBD shows: RF 2.3, RR 2.3, LF 2.2, LR 1.7 bar
• Cause: fresh puncture or leak via valve
• Fix: depends on what’s found (patch $10, tire $100+)

False Indirect TPMS

• Symptoms: TPMS light on, pressure normal everywhere (checked with a gauge)
• Cause: calibration not done after wheel change
• Fix: recalibrate (button or menu in the car) — 2-3 min

Prevention and life expectancy

• Sensor battery — 5-8 years. Car from 2018 — time to plan replacement.
• Replace all 4 sensors together — otherwise a year later you’ll do it again.
• On tire replacement — always fit a new valve (rubber seal inside the sensor).
• Don’t forget the spare — some cars have a 5th sensor.
• Winter pressure drops 3-4 psi at -20°C — may trip TPMS, top up.

Alternatives

• DIY analog: TPMS re-learn tool ($30-80) for owner-side learning
• Autel MaxiTPMS ($150+) — for ID cloning
• Car Diagnostics doesn’t program TPMS sensors (needs RF transmitter) but reads their state and warns about battery drain.

Our Prediction Agent tracks TPMS battery voltage — warns 3-6 months before full failure.

Try it on the free tier — pair an ELM327 adapter. Standard C-codes C075X on every car; detailed Mode 22 PIDs — on paid tier.