A code is not a diagnosis
A code shows which system the control module considers faulty, but not always which part to replace. The cause has to be confirmed by testing.
Common Problems
Common Problems
This section helps you understand what a symptom might mean and decide how urgently you need a shop. The descriptions are general: the diagnostic and repair procedure for your model is set by the manual and a qualified technician.
Symptom, possible cause, what to do
| Symptom | Possible causes | What to do |
|---|---|---|
| Check engine light is on | A fault detected by on-board diagnostics: sensors, ignition, exhaust system | Read the codes with a scanner through the diagnostic port; if the light is flashing or the car loses power, limit driving |
| Loud or changed exhaust sound | Burned-through muffler, leaking joints, damaged hangers | Inspect the exhaust system on a lift; do not drive if you smell exhaust in the cabin |
| Clunking from the suspension over bumps | Worn sway bar links, bushings, ball joints or shocks | Have the suspension checked; if the clunks come from the steering, do it right away |
| Soft or sinking brake pedal | Air or moisture in the system, fluid leak | Stop driving and contact a shop |
| Temperature gauge climbing | Low coolant, faulty thermostat, fan or water pump | Pull over, turn off the engine, do not open a hot coolant reservoir |
| Higher oil consumption | Leaks, engine wear, wrong oil | Check for leaks, the dipstick level and whether the oil meets the required approval |
How to work with trouble codes
Don't clear codes before an inspection
Stored codes and freeze-frame data help the technician. A code cleared without a repair usually comes back.
Catalytic converter and oxygen sensor codes
Often linked to misfires or vacuum leaks. Fixing the root cause can help the catalytic converter last longer.
Where the diagnostic port came from
- 1996
In the US, OBD-II on-board diagnostics becomes mandatory for new passenger cars starting with the 1996 model year.
- 2001
In the EU, the EOBD standard applies to gasoline cars.
- Today
Trouble codes are read with a scanner through the diagnostic port, and the malfunction indicator lamp (MIL, "check engine") alerts the driver to a problem.
Source OBD-II and EOBD on-board diagnostics standards
Sources
- Vehicle owner's manual
- OBD-II and EOBD on-board diagnostics standards
- Automakers' websites
This site does not replace your vehicle's owner's manual or maintenance schedule: take service intervals, fluid capacities, torque specs and fluid specifications only from there. Check design and emissions requirements with official sources.