P 0504 Code

Both my ABS and traction control light come on intermittently. If I turn off and restart the truck both lights are out,sometimes for minutes,sometimes for days. Brake lights work fine. What should I check/replace first. Code reader says P0504 Brake Switch A/B Correlation.

 

How is your battery. Electronics can get wonky when the battery starts to go.

 

Battery is a couple of months new. Terminals nice and clean.

 

Wouldn't hurt to have the battery load tested. Don't bother with checking the voltage with a VOM as that test only has value if you read below 12.6V

From the FSM that's available here - P0504:

 

^^^ Thank you,that PDF is going to help.

 

Opps! I guess I should have looked at the attachment above.


You probably have a defective brake switch.

DTC P0504 Brake Switch "A" / "B" Correlation

DESCRIPTION
The stop light switch is a duplex system that transmits two signals: STP and ST1-. These two signals are used by the ECM to monitor whether or not the brake system is working properly. If the signals, which indicate the brake pedal is being depressed and released, are detected simultaneously, the ECM interprets this as a malfunction in the stop light switch and sets the DTC.

HINT: The normal conditions are as shown in the table below. The signals can be read using an intelligent tester.

With the brake pedal released the STP is Off and the STP1- is On. The opposite is true when the brake pedal is depressed. If the system senses both on or off it throws this code.

Conditions
(a), (b) and (c) continue for 0.5 seconds or more (1 trip detection logic)

(a) Ignition switch ON
(b) Brake pedal released
(c) STP signal OFF when ST1- signal OFF

Causes:

• Short in stop light switch signal circuit
• STOP fuse
• Stop light switch
• ECM

 

^^^

I'd say faulty brake light switch. It's fairly common for them to intermittently work.

 

Thanks guys,I checked the brake switch today,I wish I was a leprechaun