On this page
Ignition system diagnostics looks at every link that creates a spark: the crank and cam sensors, the engine computer, the coils and the spark plugs. Route 66 Auto Repair in Upland uses this when your engine cranks but will not start, runs rough in more than one cylinder, or cuts out without warning. We find the weak link, show you the evidence and put the fix on a written estimate before any part is replaced.
Symptoms that call for a full ignition diagnosis
- The engine cranks normally but will not start.
- Stalling with no warning, then a normal restart.
- Misfires spread across several cylinders.
- A crank or cam sensor code on the scan tool.
- Hard starting when the engine is hot.
Why we test the whole chain
The engine computer needs a clean signal from the crankshaft position sensor to know when to fire. Lose that signal and every cylinder loses spark, even with perfect coils. A cam sensor fault can scramble timing. A weak power or ground feed can starve all the coils at once. That is why multi-cylinder problems rarely come down to a single coil.
We start with the symptom and work outward: is there spark at all, on which cylinders, and what is the computer seeing? Scan data, a spark tester and a lab scope answer those questions in order. Hybrid owners, tell us it is a hybrid at intake and we will explain what we can take on for your system.
Our ignition diagnostic process
Step 1: Interview
We ask when the problem happens: cold, hot, at idle, on the freeway, after fuel-ups.
Step 2: Scan and freeze frame
We read codes and the data recorded when they set.
Step 3: Check for spark
We test spark on each cylinder with a proper tester.
Step 4: Scope the sensors
We capture crank and cam signals and compare them.
Step 5: Verify power and ground
We test the coil supply and ground circuits under load.
What's included in ignition system diagnostics
Included on the work order
- 01Code and freeze frame review
- 02Spark test on each cylinder
- 03Crank and cam sensor signal capture
- 04Coil power and ground circuit test
- 05Spark plug inspection where accessible
- 06Written diagnosis with a recommended repair
How we rank ignition findings
Need now: call
- Sensor faults that cause stalling while driving
- No-start conditions
- Misfires that flash the check engine light
Need later: book
- Spark plugs approaching their service interval
- Minor connector corrosion with signals still clean
How pricing and timing work
The diagnostic fee is stated at the counter before we test and applies to approved related repair. Intermittent stalling can take longer to catch, and we tell you before extra diagnostic time is added. The repair itself depends on what failed. Your written estimate separates need-now items from things that can wait. AAA members save 10% on parts and labor, up to $75.
After the repair
We road-test under the conditions you described before release. If a stall returns, write down when it happened. Next steps may include ignition coil replacement, sensor diagnostics or an ignition system inspection at a later service.
Frequently asked questions
My car cranks but will not start. Is it ignition or fuel?
It can be either. We check for spark first, then fuel pressure and injector pulse. Knowing which is missing cuts the diagnosis time a lot.
Can a bad crank sensor cause stalling?
Yes. When a crank sensor gets hot and cuts out, the engine computer loses its timing signal and the engine stops. It often restarts once the sensor cools.
Do you work on older distributor systems?
Yes. Distributor systems use a cap, rotor and often an ignition module. See ignition module repair for those.