The transmission light and the check engine light (CEL) are both dashboard warning indicators, but they signal different types of problems—though sometimes they can overlap.
Here’s a clear breakdown of the differences and what each means:
Check Engine Light (CEL)
What It Means:
The check engine light (also called the malfunction indicator lamp, or MIL) signals that the car’s engine or emissions system has encountered a problem.
It’s monitored by the Engine Control Module (ECM).
Common Causes:
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Faulty oxygen sensor
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Loose gas cap
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Engine misfire
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Bad spark plugs or coils
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Faulty catalytic converter
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Mass airflow sensor issues
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Transmission trouble (yes, sometimes)
Key Point:
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A blinking CEL usually means a severe misfire or something potentially damaging—don’t ignore it.
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A steady CEL often means a non-urgent but important issue.
⚙️ Transmission Warning Light
What It Means:
This light specifically indicates a problem with your transmission system—automatic or CVT. It’s monitored by the Transmission Control Module (TCM) or a combined powertrain system.
Common Causes:
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Low or dirty transmission fluid
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Overheating transmission
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Sensor failure (like speed sensors)
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Slipping gears or rough shifting
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Solenoid failure
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Torque converter problems
Key Point:
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Often looks like a gear with an exclamation mark, or may say “Transmission” or “AT” (Automatic Transmission).
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Can appear separately or with a CEL if the TCM reports its issue to the ECM.
Can They Be Related?
Yes. The Check Engine Light can come on for a transmission issue, especially if it affects performance or emissions (e.g., gear slip causing improper fuel ratios).
How to Diagnose:
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Use an OBD-II Scanner:
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Plug into the vehicle and read the codes.
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CEL codes usually begin with P0xxx.
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Transmission codes may begin with P07xx or P08xx (e.g., P0700 – Transmission Control System Malfunction).
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Check Fluid Levels:
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For the transmission, check if fluid is low, burned, or dirty.
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Pay Attention to Symptoms:
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CEL + engine running rough? Likely engine-related.
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Transmission light + slipping, delayed shifting, or harsh gear changes? Transmission-related.
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What to Do:
| Light Type | What to Do Immediately |
|---|---|
| Check Engine (blinking) | Stop driving ASAP. Could damage the engine. |
| Check Engine (steady) | Safe to drive short distances—get scanned soon. |
| Transmission Light | Pull over if slipping/jerking. Get transmission fluid checked. Have a shop scan TCM. |
