Service

Engine Diagnostics

Check-engine light on? We pinpoint the problem with factory-level scan tools and real-world testing.

A check engine light means the engine control module has recorded a fault. It does not tell you which part has failed, and that distinction is where most money gets wasted on car repair. A code like P0420 does not mean you need a catalytic converter — it means the computer is seeing a reading it does not expect downstream of one, which can be caused by an exhaust leak, a failing oxygen sensor, or a misfire that is contaminating the converter.

We do diagnostics properly at All Motors Center: read the codes, look at the live data and freeze-frame conditions, then test the circuit or component before recommending a part.

What the light is telling you

Steady light: a fault is stored. Drive it, but book it. Some faults quietly cost you fuel economy for months.

Flashing light: stop driving normally and get it looked at now. A flashing light typically means an active misfire, which dumps raw fuel into the exhaust and can destroy a catalytic converter in a short distance — turning a cheap repair into an expensive one.

Light off but the car feels wrong: plenty of real faults never set a code. Rough idle, hesitation, poor economy, hard starting and stalling are all worth diagnosing whether or not a light is on.

How we diagnose

We pull all stored and pending codes from every module, not just the engine, because a transmission or ABS fault can present as a driveability complaint. Then we look at freeze-frame data, which captures the exact conditions when the fault set — engine speed, load, coolant temperature, fuel trims. That context usually tells us more than the code itself.

Fuel trim readings in particular are one of the most useful pieces of information on a modern engine. They show how far the computer is having to correct the mixture, and reading them across different engine loads distinguishes a vacuum leak from a failing fuel pump from a dirty mass airflow sensor — three very different repairs that can set the same code.

From there it is real testing: smoke testing for vacuum and intake leaks, fuel pressure and volume, injector performance, ignition coils and plugs, compression and leak-down where a mechanical problem is suspected, and scope work on sensor circuits when the wiring is in question.

Common causes we find

A loose or failed fuel cap genuinely does set an evaporative emissions code, and it is worth checking before anything else. Beyond that: failing oxygen sensors, misfires from worn plugs or coils, vacuum leaks from cracked hoses and intake gaskets, mass airflow sensor contamination, EGR faults, thermostats stuck open, and evaporative system leaks from cracked lines or a failed purge valve.

On the diesel side, aftertreatment faults dominate — see our diesel repair page for how we handle DPF, EGR and DEF problems.

Why we do not swap parts

Parts-swapping is how a $200 repair becomes a $900 one. It is also how a fault comes back three weeks later, because the replaced part was never the cause. We would rather spend the diagnostic time and be right. You get the finding explained in plain language and a written estimate before any work begins.

Call (509) 655-7715 or bring it by our East Trent shop.

What You Get

  • Factory-level scan tools, all modules
  • Freeze-frame and live data analysis
  • Fuel trim diagnosis
  • Smoke testing for vacuum and EVAP leaks
  • Misfire, ignition and fuel system testing
  • Compression and leak-down testing
  • Driveability faults with no stored code
  • Findings explained in plain language

How It Works

  1. 1Confirm the complaint and check for a flashing light or active misfire
  2. 2Scan every module for stored and pending codes
  3. 3Review freeze-frame data and live fuel trims
  4. 4Test the suspect circuit or component rather than assuming
  5. 5Explain what failed, why, and what it costs to fix
  6. 6Carry out the approved repair
  7. 7Clear codes, run the drive cycle and confirm readiness monitors pass

Frequently Asked

What does a check engine light actually mean?

It means the engine computer has stored a fault. It does not identify a failed part. A code points at a system, and the actual cause has to be tested — which is why the same code can lead to three very different repairs.

Is it safe to drive with the check engine light on?

A steady light usually means you can drive, but you should book it, since some faults quietly cost fuel economy for months. A flashing light means stop driving normally and get it seen now — that typically indicates an active misfire, which can destroy a catalytic converter within a short distance.

Can I just get the code read for free at a parts store?

You can, and it will tell you the code number. What it will not tell you is which component failed, because that requires live data and circuit testing. A free code read is a starting point, not a diagnosis, and acting on the code alone is how people end up buying parts they did not need.

My car runs badly but there's no light. Can you still help?

Yes. Plenty of genuine faults never set a code — rough idle, hesitation, hard starting, stalling and poor fuel economy among them. Those are diagnosable and worth bringing in whether or not a light is on.

Does a P0420 code mean I need a new catalytic converter?

Not necessarily, and this is one of the most common expensive mistakes. P0420 means the computer sees an unexpected reading downstream of the converter, which can be caused by an exhaust leak, a failing oxygen sensor, or a misfire contaminating the converter. We test before recommending a part that expensive.

How long does diagnostics take?

Straightforward faults are often identified within an hour. Intermittent problems, electrical faults and anything that only appears under specific conditions take longer, because they have to be reproduced before they can be confirmed. We will tell you what we expect up front.

Other car and light-truck work we do

We cover the greater Spokane area and North Idaho — see the areas we serve.