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Juan Crespo
Juan Crespo, ASE Certified Technician
Category: Chevy
Satisfied Customers: 1526
Experience:  A.S.E. Master Technician, Advanced Level, Emissions - Asian, Domestic, & European
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C0045 speed sensor, have ohmed out the harness, replaced the

Customer Question

C0045 speed sensor, have ohmed out the harness, replaced the speed sensor, checked the tone ring, cleared the code, code comes right back. Getting no signal from the left speed sensor
JA: Do you know where your speed sensor is located? Do you have a voltmeter to check the sensor?
Customer: Yes and I have checked the volts, but it goes away when the code resets
JA: What year is your C300?
Customer: It's not a c300, It's a 2009 chev Silverado k1500
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: Replacing the speed sensor 2x, just to make sure the new one wasn't faulty. Checked voltage, checked tone ring on the rear axle.
JA: Anything else you think the mechanic should know?
Customer: Have checked the voltage from the EBCM back to the sensor, all good with the key on, but voltage disappears when the code reappears
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the Chevy Mechanic about your situation and then connect you two.
Submitted: 1 year ago.
Category: Chevy
Expert:  Juan Crespo replied 1 year ago.

Hi there.

The system is designed so voltage will disappear if a fault is detected with the sensor circuit.

Even with a new sensor, if the signal is not there or not right, the EBCM will set a code. The most probable cause of this issue is something to do with the encoder ring; could be dirt, debris or it could be cracked or broken acting as insulation. The key here is to use a scope or very fast multimeter to verify the signal is indeed being generated - when the magnetic encoder ring rotates and passes by the wheel speed sensor head; it generates a sine wave in the wheel speed sensor. The wheel speed sensor converts this analog signal to a digital square wave, and typical digital signal values switch between 7mA (Low) and 14mA (High) DC current. If the signal is verified as being generated at the sensor, the next step is to check the wiring from the sensor to the EBCM. However if the signal is verified going all the way to the EBCM, if the code resets, then the fault lies with the EBCM itself.