Check engine light 2021 CX5
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Junior Member
Joined: Jan 2021
Posts: 15
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From: Lehigh Valley PA
Check engine light 2021 CX5
Greetings
Changed the plugs on my wife's 2021 cx5 signature 2.5T with 50k miles. I'm getting a flashing check engine light, Driver Attention alert system malfunction, smart brake system malfunction & front radar sensor malfunction. Engine has a miss ~1500 rpm. I've checked the engine compartment for a hose or connector that I didn't re-connect but can't see anything out of place. Took car for a short ride and was lucky to get back to the garage. I used NKG Dilkar7M8 plugs. Will check engine compartment again in the AM. Anybody have any thoughts? thanks
Changed the plugs on my wife's 2021 cx5 signature 2.5T with 50k miles. I'm getting a flashing check engine light, Driver Attention alert system malfunction, smart brake system malfunction & front radar sensor malfunction. Engine has a miss ~1500 rpm. I've checked the engine compartment for a hose or connector that I didn't re-connect but can't see anything out of place. Took car for a short ride and was lucky to get back to the garage. I used NKG Dilkar7M8 plugs. Will check engine compartment again in the AM. Anybody have any thoughts? thanks
Senior Member
Joined: Oct 2018
Posts: 10,515
Likes: 216
From: Northern California
It would help is you checked your ECU
A DIY unknowing can forget that there are 5 parts to the ignition when doing a simple spark plug change .
spark plug
coil
spark plug boot
boot spring
coil connector
I any are damaged or not installed correctly can cause several problems…Some are what post 1 are describing.
At 50k miles the following should have been changed along with the spark plugs.
Spark plug boots
Boot springs
Dielectric grease should be used sparingly on the spark plug boots at the end to allow the boot to slide over the insulator so the terminal will connect properly and securely to the boot terminal connector . Failure to have a good spark plug to connect contact can cause problems like mentioned in the first post.
Continued running the engine even for a short time with either of these issues can cause coils to fail or reduce their output again causing problems as mentioned.
Scanning the ECU in the 3 main areas is essential to get an idea where to start looking to resolve the problem.
Lastly while it does not happen often it is easy to damage the insulator of the spark plug during installing it which can cause problems . The only way to determine that is removing and carefully inspecting them or to use an oscilloscope and look at the wave pattern .
A DIY unknowing can forget that there are 5 parts to the ignition when doing a simple spark plug change .
spark plug
coil
spark plug boot
boot spring
coil connector
I any are damaged or not installed correctly can cause several problems…Some are what post 1 are describing.
At 50k miles the following should have been changed along with the spark plugs.
Spark plug boots
Boot springs
Dielectric grease should be used sparingly on the spark plug boots at the end to allow the boot to slide over the insulator so the terminal will connect properly and securely to the boot terminal connector . Failure to have a good spark plug to connect contact can cause problems like mentioned in the first post.
Continued running the engine even for a short time with either of these issues can cause coils to fail or reduce their output again causing problems as mentioned.
Scanning the ECU in the 3 main areas is essential to get an idea where to start looking to resolve the problem.
Lastly while it does not happen often it is easy to damage the insulator of the spark plug during installing it which can cause problems . The only way to determine that is removing and carefully inspecting them or to use an oscilloscope and look at the wave pattern .
Last edited by Callisto; Apr 2, 2026 at 11:49 PM.
Thread Starter
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Junior Member
Joined: Jan 2021
Posts: 15
Likes: 0
From: Lehigh Valley PA
Callisto thanks for your suggestions. Local parts house did not have the boots and springs in stock, has to order them. In the meantime, I removed them, cleaned and re-installed. The warnings went away and the test drive was good. Wife will be the final judge as to the performance as she is the main driver. Thanks again
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