Has your car been hard to start lately, especially when cold? A faulty cold start or engine coolant temperature (ECT) switch could be the cause of this starting difficulty. Read on to learn how to tell if your cold switch is bad, understand how it works, and to test your car cold start switch.
Table of Contents
- What is a Cold Start Switch?
- Key Signs Your Switch is Failing
- Locating the Cold Start or Coolant Switch
- How to Test Your Cold Start or Coolant Switch?
- 1. Locate and access your cold start switch.
- 2. Disconnect the switch harness.
- 3. Set multimeter to continuity test setting.
- 4. Touch probes to switch terminals.
- 5. Listen for continuity tone.
- 6. Warm up the sensor slightly.
- 7. Retest switch terminals.
- 8. No tone means it’s working.
- 9. Replace if tone remains steady.
- Fixing a Faulty Cold Start or ECT Switch
What is a Cold Start Switch?
The cold start switch, also called the ECT sensor, detects your engine’s temperature. It communicates this data to your vehicle’s computer.
When cold, it triggers a richer fuel mixture. This extra fuel helps fire up a cold engine. Once warm, this richer mixture is no longer needed.
Key Signs Your Switch is Failing
A failing cold start switch causes various issues when starting up cold. Pay attention for these four key problems:
1. Long Cranking Time
Turn the key, but your engine cranks and cranks without starting. This extended cranking drains your battery over time.
Why? Your computer isn’t getting the “cold engine” signal. So it fails to trigger the added fuel needed to start.
2. Intermittent Stalling
Does your car sometimes stall out after cold startup? With a faulty switch, that quick stall-out becomes more common.
Without the right fuel mix, your engine may start but runs rough. That leads to stumbling and cutting out completely.
3. Poor Mileage After Cold Starts
Fuel mileage should improve as your engine warms up. With a bad switch, your mileage stays irregular even after warming.
Why? The engine continues running that too-rich cold start fuel mix instead of transitioning to a leaner warmup ratio.
4. Misfiring or Rough Idle When Cold
Listen for that rough, unstable idle on initial startup. The engine may even misfire completely on one or more cylinders.
This happens because the faulty switch fails to trigger the vital cold-start fuel enrichment needed.
Pay attention because even one of the above symptoms can indicate it’s time to test your cold start switch.
Locating the Cold Start or Coolant Switch
You’ll need to locate your cold start switch to test it. Here’s a quick look at where to find it on a few common vehicles:
GM Vehicles – Mounted on the thermostat housing found on the engine near the radiator hose.
Ford Models – Also mounted on the thermostat housing, commonly on the driver’s side of the engine.
Toyota and Hondas – Located along the firewall or etched “ECT Sensor” on the engine.
European Models – Near the main engine wiring harness, often under the intake manifold.
Now let’s move on to testing it.
How to Test Your Cold Start or Coolant Switch?
Testing your switch is a fast and straightforward process. All you need is a digital multimeter capable of testing for continuity.
Safety Note: Ensure the ignition is OFF before beginning any testing procedures.
Here is the simple step-by-step:
1. Locate and access your cold start switch.
Refer to your vehicle repair manual. Follow any steps needed to gain access the switch and wiring connector.
2. Disconnect the switch harness.
Find the wiring harness leading from your car’s computer to the switch. Pull it off the switch connector.
3. Set multimeter to continuity test setting.
Turn knob to continuity checker symbol, which looks like waved lines bookended by vertical lines. You’ll hear a tone if a complete circuit is detected.
4. Touch probes to switch terminals.
With engine stone cold, touch the multimeter probes to each switch terminal one at a time.
5. Listen for continuity tone.
If working correctly, you SHOULD hear a steady tone at this cold temperature. This confirms a complete circuit exists when cold.
6. Warm up the sensor slightly.
Carefully warm the switch to around 100 degrees Fahrenheit using a hair dryer or hot water. Avoid exceeding 140 degrees.
7. Retest switch terminals.
Touch the multimeter probes to each switch terminal again. Listen closely now.
8. No tone means it’s working.
If functioning properly, continuity is NOW broken as it warms up. You should hear NO tone at this point.
9. Replace if tone remains steady.
Hear that same unbroken tone? That constant continuity means the switch has failed. It’s staying stuck in cold mode even when warm. Time to replace it!
And checking your switch is as straightforward as that.
Fixing a Faulty Cold Start or ECT Switch
DIY-savvy owners can replace their own cold start switch in less than an hour. You’ll need these steps:
1. Review repair manual to access switch safely.
2. Disconnect harness connector and detach switch from housing. Compare to new unit.
3. Clean mating surface completely. Use a wire brush and electrical cleaner.
4. Apply dielectric grease to new switch O-ring. This ensures a good seal.
5. Connect new switch connector. Listen for an audible click.
6. Refit any components moved to access it.
7. Clear any engine codes. Drive and confirm issue is fixed.
If this seems beyond your skill level, have a professional mechanic complete the fast and affordable repair instead.
Pay attention if your engine seems increasingly hard to fire up when cold. Extended cranking, rough running, and poor performance are all signs of a failing cold start or ECT switch.
Testing the switch takes just minutes with a multimeter in your garage. Repairing or replacing the faulty switch gets your vehicle reliably up and running again.
Don’t hesitate to replace the switch if you confirm it’s no longer working properly. Allowing the issue to continue will strain your engine over time while making daily driving a pain. With simple testing procedures and an inexpensive repair cost, restoring peak starting performance pays greatly while cruising your vehicle down the road.