Sprinter 4-Cylinder OM651 Losing Coolant, Limp Home Mode – READ THIS!

We have seen an increasing number of 4-cylinder powered Sprinters (OM651 engine) experiencing coolant loss, “limp-home mode”, and eventual widespread engine issues ranging from temperature control problems to power loss. We’ll go over what is happening, causes and repair procedures in this article.

Common codes related to this problem:

P0003313 - Charge Air bypass flap open circuit
P0299FA - Boost Pressure Turbocharger 1 too Low
P0299FB - Boost Pressure Turbocharger 1 too Low
P226100 - bypass flap 'charge air' has a mechanical malfunction
P261F71 - recirculation pump has failed or actuator is blocked
P012800 - coolant temperature below specified threshold
P012809 - coolant temperature below specified threshold. There is a component failure
or "Limp Home Mode" condition

Basic Description of Problem

All these codes are the result of coolant getting into the vacuum system. The vacuum system controls the turbocharger actuator, boost actuator, heater control in the cabin air system and brake booster, so all these are affected once coolant contaminates the vacuum system. The vacuum system itself, including the reservoir and pump, will also be affected.

This problem affects Sprinter vans more often than Mercedes models. Failure rate is commiserate with load – so loaded 3500 models with 4-cylinder engines are much more likely to experience this than E250 sedans.

Cause of the Problem

In order to help engine warm-up, Mercedes uses a water pump that has a movable impeller. The impeller can move into and out from a shield, which decreases and increases coolant flow, respectively.

The position of the pump is controlled by the vacuum system. A common failure mode of the pump is coolant leaking by the shaft seals. The coolant then escapes into the vacuum diaphragm in the water pump. Eventually the diaphragm fails, and coolant is then sucked into the control valve and ultimately the entire vacuum system.

Symptoms of the Problem

The first symptoms of water pump failure and coolant getting into the water pump vacuum diaphragm is loss of temperature control. If your Sprinter is experiencing temperature control issues and throwing codes like P012800 or P012809 it can be an indication that coolant is in the water pump control diaphragm and the water pump has failed.

Once the coolant gets into the vacuum system multiple systems will start to fail, including turbocharger boost pressure. Codes P0299FB and P0299FA are both boost pressure codes that may indicate the coolant has reached the boost pressure control valves.

Diagnosis

Coolant loss and power loss together is a pretty clear indication this known problem is happening, but there are a few ways to double check and be sure.

Review all vacuum lines and look for wetness at the connections. If none is found, remove the lines attached to the vacuum reservoir first and check for wetness. You can also slightly pressurize the vacuum system (do not exceed 14 PSI!) to check for leaks.

Repair Procedure

Obviously the first step is to replace the water pump. Aftermarket replacement water pumps may be available *without* the vacuum controlled impeller, which eliminates this problem altogether. However, this means your Sprinter will warm up slower in the cold months, which may or may not be important to you.

You will also need to repair the vacuum system to remove all the coolant. This requires replaces the vacuum reservoir as it is likely full of coolant. The reservoir is sealed and cannot be opened and drained, so it must be replaced. You will also want to replace the vacuum changeover valve (or solenoid) for the water pump as coolant contamination has likely ruined the valve. Remove all other vacuum lines, check for and drain any coolant found.

Repair Shopping List

Vacuum Reservoir OM651 – 6510700768
Vacuum Changeover Valve OM651 – 0025407097
Water Pump OM651 – 6512001602
Vacuum Pump OM651 – 6510900005

Reference Items

LI07.09-N-06338

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