After searching through the mountain of C5 C1243 code ECBM posts for 01-04 C5’s and reflowing the solder connections for the relay on my ECBM, I’ve concluded that the suspect solder joints for the relay were not the issue. Before tearing into the ECBM, I cleaned both frame rail ground points and there was zero corrosion inside the plugs or at the ground points.

Further testing at the BPMV two pin connector at the ECBM revealed the following (ignition on, engine not started)

I get a few seconds of + at the forward connection. I get nothing at the rear connection, which should be – . Obviously the momentary + would spin the pump and pass the power on test if the other pin was supply the negative side which would enable the pump to run.

I tested the motor with 12 volts and it spins right up without issue. The missing negative is preventing the motor from spinning and presumably causing the 1243 code, BPMV Pump Stalled.

I pulled the cover off the ECBM and checked continuity between both BPMV pins at the female connector and the solder lug on the board and got good conductively.

From here on I’m at a loss. The ECBM electronics are potted and I can’t tell how the BPMV - pin would get the negative side ?

At this point I’m wondering if there is an internal issue with the IC within the ECBM or something else is the issue.

2002 C5Z, 25K miles, 2X yearly brake fluid changes.

 

The relays are also known to go bad.

 

I did a bit more testing...appears I AM getting the 0.3 second negative voltage to the pump. Just hard to measure due to the very short duration. The relays appear to be okay. I'm not suspecting the pump may be drawing too much current. I'm testing that tonight.

 

Update...true to the code, the issue was the ABS pump stalling or drawing excessive current. After powering up the motor direct, i could hear it labor initially and after 15-20 seconds it smoothed out and ran normally. I repeated this several time and put the ECBM back on the BPMV and fired up the engine and the code is gone. This car does a lot of sitting...like 6 months at a time, and I NEVER drive with traction control or active handling activated, which I'm sure contributes to this issue since the BPMV never runs. . the brake fluid is changed at least once a year so that should not be a factor as the fluid comes out of the calipers and looks new (Tech 2 cycled).. I realize this may be temporary and that the motor may end up needing replacement but the ECBM is fine.