Brake and ABS problems

[02V70]

I get a brake failure stop safely message, and the brake, abs, check engine, and skid lights are on. Along with a yellow exclamation triangle in the middle. Cruise control, and the trip odometer also don't work.

I got the codes scanned, and there were around 15 codes, but they said it was probably due to the battery dying, and being disconnected. Here were the other codes.

1A5F:
Definition:
Communication With The Brake Control Module (BCM). Signal Missing
Description:
The diagnostic trouble code (DTC) is stored if the central electronic module (CEM) registers that communication with the brake control module (BCM) is not operating. The diagnostic trouble code (DTC) can be diagnosed when the ignition has been on for more than 10 seconds. ABS warning lamp lit. Note! In the event of CEM-1A5X diagnostic trouble codes (DTCs), the central electronic module (CEM) must not be replaced as the diagnostic trouble code (DTC) indicates a communication fault in the controller area network (CAN)

9400:
Definition: Brake Pedal Position Sensor, Faulty Signal.
Description is long, but its here: https://www.dtcdecode.com/Volvo/ECM-9400

510F:
Definition:
Speed Signal, Faulty
Description:
Diagnostic trouble code (DTC) ECM-510F is stored as a result of an error message is sent to the engine control module (ECM) if a fault in the vehicle speed signal has been detected in the ABS control module. NOTE: The diagnostic trouble code for this fault is first generated in the brake control module (BCM) and then in the engine control module (ECM). This diagnostic trouble code cannot be cleared until the code in the brake control module (BCM) has been remedied and cleared.

6000:
Definition:
A/C Relay. (Signal Too High Or Too Low)
Description:
This diagnostic trouble code (DTC) is stored if the engine control module (ECM) registers a short-circuit to ground or supply voltage or an open-circuit in the control signal cable for the air conditioning (A/C) relay.



After they cleared the codes, I drove around until the check engine light came on again, and had the codes scanned again. This time, they had a much less fancy code reader because their fancy one was "updating."

The codes that one gave were:



p0504:
The P0504 code is defined as “Brake Switch A/B Correlation” and is a generic diagnostic trouble code (DTC) generated by the engine control module (ECM) of your car.
P0504 indicates that the ECM has detected a malfunction in the brake light switch signal circuit (stop lamp or stop light switch circuit).

p0571
P0571 is a generic OBD-II diagnostic trouble code (DTC) that the engine control module (ECM) generates. The P0571 code is defined as a “cruise control / brake switch ‘ A’ circuit malfunction.”

How would I continue diagnosing this issue? Based on the codes, is there a part that I can test or replace?

[abscate]

You need something thst can get to the Volvo codes, format ECM-xxxx and BCM-xxxx to get better info on those failures. If you are in Southern CA I’ll be in Laguna Beach in a few weeks , I can bring my big boy AUTEL

[vtl]

You need this: https://www.fcpeuro.com/products/volvo- ... e-30742306 A typical wear item on all P2 Volvos.

BCM communication error is suspicious. Could be a battery-related glitch, or CAN-bus problems, or bad relay in CEM that powers BCM.

[02V70]

The mechanic that worked on it previously (they are the worst mechanic I have ever had) mixed up a bunch of fuses, and some of the relays were missing from under the hood. The car only started to have this (and many other) problems after it was taken to them. They could have also F'ed with the relays and fuses on the CEM, however, I do not have a diagram of it, nor can I find one. Does anyone know where I can find it?

[vtl]

Google TP3961202.pdf, this is a dump of EWD (Electronic Wiring Diagrams) for 2002 V70.

Also VIDA has a lot of good info, like connector pin outs, principles of operation, etc.

[02V70]

I took a look at the BCM connector and the plastic thing that covered it was broken. I couldn't figure out how to get the harness disconnected, but I did wiggle it around a little and pressed those pins/sliders in. They were kind of in the middle, so I'm not sure if they are supposed to be in or out. This fixed the issue, and the only thing left is the check engine light, and the yellow warning light in the middle.

[02V70]

After driving a bit, the check engine light is now off.

Also, there is a message that says Airbag Service urgent. How do i get rid of the message?

[jonesg]

you need a decent code reader to reset the airbag light.
Not disconnecting the battery when playing around with elec system sets this code.
Its well worth your money to get vida on a laptop.
The vida forum can help and theres usually someone selling them.