C1203 – All makes

Code : C1203
Make : All makes
Description : C1203 ECM Communication Circuit Malfunction
Possible causes :
– The wrong ECU or sensor was installed
– Skid control ECU (Brake booster with master cylinder assembly)
Solutions :
– Carry out a Reset via CarDiag
– Choose a better quality fuel
– Check that the tank cap is securely closed
– Check the oil level and add more if it is lower than MAX
– Restart an Automatic diagnostic via CarDiag
– If the fault persists, you can check the “Possible causes” listed above : visually inspect (by yourself (tutorials to come) or by a professional) the wiring harness and the associated connectors, check for damaged components, and look for broken, bent, pushed, or corroded connector pins.

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