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P0504 Diagnostic and Repair Guide for 2006 Chevrolet 5500 Bucket Truck

Model: 2006 chevy 5500 Fault Code: P0504 Posted: 2007-06-06 09:21

Hi everyone, I'm currently experiencing a P0504 brake switch A/B correlation fault on my 2006 Chevrolet 5500 bucket truck. This vehicle is used by an electric utility company for service work and does not have a trailer brake module. I've confirmed the issue using OBD-II scanner tools, but my diagnostic software only supports up to the 3500 series. The check engine light activates intermittently — sometimes during operation, other times not — and when it does come on, the chime sounds and hazard flashers activate. The truck is still under warranty, which makes troubleshooting tricky since we've already had two units in the shop with similar issues. It's currently not safe to drive into service due to this fault. I’ve confirmed that brake lights function properly and speed control disengages when braking. However, no ABS-related warning lights are present. I'm seeking detailed input on possible root causes — especially whether a faulty clock spring in the steering column could be responsible for the P0504 code, given that the brake signal is used to disable speed control via the steering column wiring. Any confirmed fixes or diagnostic steps specific to this model year and application would be greatly appreciated.

Related fault codes
P0504
Comments (11)
Anonymous 2007-06-08 06:40

Has anyone else encountered a P0504 code on a 2006 Chevrolet 5500? If so, what was the root cause or repair process?

Anonymous 2007-06-08 08:16

A faulty trailer brake module could be a potential source — but this is a bucket truck used for utility work and does not pull trailers. This makes that less likely.

Anonymous 2007-06-08 14:12

I've confirmed no trailer brake module is installed on this unit; it's strictly a bucket truck used by an electric company. I don't believe trailer-related systems are involved here.

Anonymous 2007-06-09 06:06

A brake switch failure could be the cause — but the absence of ABS warning lights suggests this isn’t related to anti-lock braking system issues.

Anonymous 2007-06-11 08:17

No, it's not an ABS issue. The check engine light is the only one that activates, and it does so intermittently. I've been monitoring it closely during daily operations.

Anonymous 2007-06-11 08:24

Do brake lights function normally? Does speed control disengage when braking? Is there a known issue with the steering column or clock spring that could interfere with brake signal transmission?

Anonymous 2007-06-12 07:39

The truck departs every morning at 8:00 AM and returns between 3:30 PM and 4:00 PM. I’ve confirmed all lights are checked before departure, so the issue appears to be intermittent or triggered under specific conditions.

Anonymous 2007-06-12 09:52

Thanks for clarifying — I was just wondering if there might be an ABS-related symptom, but it seems absent in this case.

Anonymous 2007-07-20 06:10

Still experiencing the same P0504 issue. After a test drive of about 10 miles, no ABS issues or pulling were observed. The check engine light only activated intermittently — and when it did, the chime and hazard flashers turned on. Crew members reported that it didn’t activate yesterday, suggesting it's not consistent. This points to a possible intermittent wiring or sensor issue.

Anonymous 2007-07-20 07:06

The hazard flashers — meaning turn signal/hazard lights — activating when the brake is applied could indicate a clock spring failure in the steering column. The brake signal typically travels through the clock spring to disable speed control. I recommend testing this by rotating the steering wheel to its full left and right extremes during a test drive, especially before returning the truck to service.

Anonymous 2007-07-20 07:36

That's an excellent point — I hadn't considered that. I'll try rotating the steering column to its limits when the truck returns today to see if it resolves or triggers the issue.