BMW exhaust fluid warning
This TSB applies to BMW models E70 and E90, equipped with the M57Y diesel engine. The customer receives a warning message that the diesel exhaust fluid is low and that the engine will not restart in 999 miles or less. The warning activates a few thousand miles prior to the recommended oil service.
Cause 1: Diesel exhaust fluid (DEF) was not properly refilled during the previous service. The Selective Catalyst Reduction (SCR) system has used-up the remaining DEF.
Cause 2: There was no DEF transfer from the passive tank to the active tank. Fault code 46EB (Reducer inter-tank pump unit) may also be stored in the DDE.
Follow BMW service procedure SI B16 01 09 to properly drain and/or refill the active and passive tanks of the SCR system. Current BMW models require approximately 6 gallons of DEF during refill. The system must be drained and filled with fresh DEF at every engine oil service. Problems caused by an improperly maintained SCR system is not a warranty matter.
Check the fill levels of the passive and active tanks. If the active tank is empty and the passive tank is full, there has been no transfer of DEF. There could be several reasons for a no-transfer condition:
The DEF transfer pump is not working properly. Check the operation of the transfer pump using ISTA/D test plan “B1365_D7SCRTPMP SCR: transfer pump.” The test will run the transfer pump until the active tank is full. If the active tank has been filled before this check, it will be necessary to drain a minimum of 0.5L (1 pint) of DEF from the active tank. Check to verify if the pump runs, and if it transfers DEF. Look for signs of DEF leaking out of the electrical connector on the pump (internal seal failure of the pump). On cars with low mileage, there is the possibility that the transfer pump is dry and will not create enough suction to transfer the DEF (fault code 46EB will also be stored).
Run this test to activate the transfer pump, but with the feed line to the active tank disconnected from the transfer pump. The pump will be able to create enough suction at this point to start transferring. Once the pump does transfer DEF, it will no longer need this priming action to pump DEF. Fault code 46EB can only be deleted after the activation of the refuel detection. This should be done with service function “B1365_D7SCRRES Activate Refuel Detection.” Both tanks must be refilled before running the refuel detection. Now the fault memory can be deleted.
There is a break or disconnection in one of the DEF lines to or from the transfer pump. Check the DEF lines and connections at the passive tank; from the passive tank to the transfer pump; and from the transfer pump to the active tank. Check for loose connections, cut or pinched lines.
There is a restriction or blockage at the check valve on the transfer line at the active tank. The amount of DEF transferred is based upon a given flow rate of the pump, not by volume. If there is a restriction or blockage in the line, the correct amount of DEF will not be transferred.
The DEF in the passive tank is frozen. If the outside temperature is 25 degrees F or lower, the DEF will freeze. If this lower temperature lasts for an extended period of time, the DEF in the passive tank will never fully thaw, and transfer of fluid will cease. Only he DEF in the active tank will be utilized for the SCR injection. A full active tank will have enough DEF for approximately 3,000 miles of driving. If freezing is found to be a root cause, inform the customer that he or she may be required to top up the active tank periodically until the DEF in the passive tank has thawed.