Time for an update - but it's not very good news I'm afraid.
First a bit of background info:
On BMW models with the N52 or N54 6-cylinder engine, the coolant pump is an externally mounted electric pump bolted to the right front of the engine block. Using an electric pump (as opposed to the engine-belt-driven variety) helps engine cooling efficiency and longevity, as the pump can operate regardless of whether the engine is running or not and also regardless of engine rpm. For example, a low rate of flow is maintained during cold start situations to help the engine warm up rapidly, while a high flow rate can be used for rapid cool-down, such as when the engine is shut off.
The electric coolant pump is controlled by the engine control module (ECM). Engine load, temperature, operating range and other factors are used by the engine management system (DME) to determine coolant pump operation and speed. The pump also has self-diagnostic capabilities. Fault codes for the following conditions are stored in the ECM and can be used for diagnosis:
• Pump impeller speed deviation
• Pump shaft stiffness or obstruction by foreign object
• Incorrect water / coolant mixture
• Air in the cooling system
You can see the pin-out info for the pump here...
The DME line uses BSD (bit serial data) to both send control signals to the pump and also receive diagnostic info. The drive signal looks to be around 1KHz, probably PWM based but the waveform looks complex with different mark space ratios integrated into it.
I should mention that this pump was faulty ("implausible pump speed") so it may not be operating in a normal way at all.
I began by just applying power to the relevant pins (+12V on pins 1 & 3, 0v on pin 4). On switch on the pump spins up and does some strange pulsing (>50A input current pulses
), it repeats this around 10 times or so and then settles down at a steady speed and runs continuously.
I then applied 1KHz square wave pulses to pin 2. This did change the speed of the pump a little. I then started to adjust the duty cycle of the waveform which did indeed change the pump speed but not very consistently and certainly not how I would have expected, and also over quite a limited range. I played around with the frequency a little but again the pump behaved strangely and kind of rebooted itself and went back into pulsing mode.
All pretty inconclusive in terms of operation, but again this pump may be faulty. The bad news is the electronics are completely unserviceable. They are all potted into a module and then the module itself is glued into the housing with what feels like nuclear cement. Not much chance of a cheap fix here guys I'm afraid
North West Surrey
