Why does it start again after it cools down?

Because the failure is thermal. As the sensor's internal components heat up, their electrical characteristics drift out of range and the signal is lost. Cooling brings them back into range, so the car runs perfectly until it heats up again.

Can I keep driving it?

Not safely. An engine that shuts off at speed takes power steering assist and brake boost with it. Keep trips short and local until it is fixed.

Why didn't the shop find anything?

Because they tested it cold. Tell them explicitly that it only happens after 20 minutes of driving on a hot day, and ask them to keep the car long enough to reproduce it or to test with heat applied to the suspect sensor.

Cause library

Heat-sensitive sensor failure

A crankshaft or camshaft position sensor that works cold and drops out once under-hood temperature climbs.

Written and reviewed by Nicholas Velez, Founder, Car Dogs · Updated August 24, 2026

What this actually is

The crankshaft position sensor tells the engine computer exactly where the pistons are. Without that signal the computer cannot time spark or fuel, so the engine simply stops — no warning, no stumble, just off. The camshaft sensor plays a similar role and is needed for starting on most engines.

These sensors fail in a distinctive way. As the internal windings heat up, resistance climbs and the signal degrades. Cold, the sensor works perfectly. Twenty minutes into a July drive in Hesperia, it drops out. Let the car sit for half an hour and it starts and runs fine again — which is exactly why so many of these cars pass a shop test.

That intermittent, heat-dependent pattern is the single most useful thing you can tell a technician, because a cold car on a lift will not reproduce it.

This page explains one possible cause. It is not a diagnosis of your car — only a hands-on inspection can confirm what is wrong with yours.

Stop driving / urgent

A car that shuts off without warning at freeway speed loses power steering assist and power brake assist immediately. This is a safety issue, not an inconvenience. Do not commute the I-15 or the 210 on it while you wait for an appointment.

How it fails

Internal winding or electronics failure that only appears above a temperature threshold
A cracked sensor housing letting oil in, common on high-mileage engines
A damaged reluctor wheel or tone ring giving an erratic signal
Wiring or connector damage where the harness passes near the exhaust
A failing ignition switch or relay, which imitates this exactly and is much cheaper

Symptoms this causes

If any of these match what your car is doing, start with that page — it walks the whole pattern, not just this one cause.

Stalls while driving

Engine & performance

A car that shuts off while you are driving takes power steering and brake assist with it. This is the one drivability complaint we treat as urgent every time, regardless of how well it runs the rest of the day.

Read the symptom guide

Car won't start

Battery & electrical

Clicking, slow cranking, or dead silence each point somewhere different. Diagnose it by ear before you pay anyone.

Read the symptom guide

Check engine light

Engine & performance

A code is a clue, not a diagnosis. What the light means, and how to keep a scan from turning into a parts cannon.

Read the symptom guide

What you can check yourself, free

None of this requires tools you do not already own, and all of it makes the shop conversation shorter.

Log every stall: how long the car had been running, ambient temperature, whether it was at idle or at speed
Note whether it restarts immediately or only after cooling for 20 to 40 minutes — the cooling requirement is the key clue
Note whether the tachometer drops to zero the instant it dies, which suggests a lost crank signal
Check whether a check engine light is stored even though the light may not be on now

The tests that actually prove it

Ask for these by name, and ask to see the results. A measurement is a diagnosis; a guess is a parts bill.

Freeze-frame data from any stored code, showing coolant temperature and load when the fault set
A hot-condition test: the shop must reproduce it warm, sometimes with gentle heat applied to the sensor
Live crank and cam signal watched on a scan tool or scope during a stall event
Fuel pressure monitored at the same time, because a hot fuel pump failure looks identical from the driver's seat

What it should cost

Repair	Typical range
Diagnosis, including reproducing the fault hotLegitimately harder than a normal scan. Expect real time to be billed.	$140-$300
Crankshaft position sensorCheap part, occasionally awkward access.	$220-$550
Camshaft position sensorUsually accessible on the front of the cylinder head.	$200-$480
Harness or connector repairCommon when the wiring runs near the exhaust manifold.	$150-$400
Fuel pump (the main alternative diagnosis)Should only follow a fuel pressure test taken during an actual stall.	$650-$1,400

Repair costs vary by vehicle, location, labor rate, and parts. Treat every range as a starting point for a conversation, not a quote.

Estimate your repair cost

What to push back on

These are the quotes we see most often attached to this cause that the evidence did not support.

A sensor replaced solely because a code named it, with no live signal test
A fuel pump and a crank sensor replaced in the same visit as a shotgun approach
A diagnosis reached entirely on a cold car when your complaint is heat-related
'We could not duplicate it' followed by a parts bill

Questions to ask before you approve work

What did you find, and what test confirmed it?
Is this a safety item, or can it wait?
What happens if I wait a month?
Which part actually needs replacing, and why that one?
Can you show me the failed component or the measurement?
Was anything else damaged by this?
What is the diagnostic fee, and does it come off the repair?
Is any of this quote optional or recommended rather than required?

Questions people actually ask

Why does it start again after it cools down?: Because the failure is thermal. As the sensor's internal components heat up, their electrical characteristics drift out of range and the signal is lost. Cooling brings them back into range, so the car runs perfectly until it heats up again.
Can I keep driving it?: Not safely. An engine that shuts off at speed takes power steering assist and brake boost with it. Keep trips short and local until it is fixed.
Why didn't the shop find anything?: Because they tested it cold. Tell them explicitly that it only happens after 20 minutes of driving on a hot day, and ask them to keep the car long enough to reproduce it or to test with heat applied to the suspect sensor.