Diesel Return Flow Sensor RFS400

Diesel Return Flow Sensor RFS400

Common Rail diesel injection systems become more and more advanced nowadays. In order to detect a malfunction in this system, measurements have to be much more accurate. Introduction of pressurized return flow systems makes measuring the return flow using open "jars" impossible.

The Diesel Return Flow Sensor RFS400 is a closed system four channel flow sensor that can be placed in the return flow circuit of a Common Rail diesel engine. Connected to the Automotive Test Scope ATS5004D with ATIS software, the small return flows of four cylinders can be measured simultaneously and accurately. A graph for each cylinder shows the size of the fuel flow. Due to the closed system, no diesel is spilled, keeping the work area clean. It also makes it possible to perform measurements while driving the vehicle.

Order code: TP-RFS400
Price: 577.80

Performing a diesel return flow measurement

Category: Miscellaneous

The table below shows detailed specifications of the Diesel Return Flow Sensor RFS400.


Flow range0.2 ml/min to 145 ml/min
Accuracy5 %
Output4.5 V = 145 ml/min, 0.2V = 0.2 ml/min
Operating fuel pressure1 to 10 bar
Connection2 x 4 mm banana socket per channel


Connectionfixed cable with isolated alligator clips
Voltage9 to 30 V DC
Current20 mA @ 12 V


Width64 mm
Height39 mm
Length128 mm
Power cable length100 cm
Fuel hose length42 cm
Weight530 g


Operating temperature-10 to 80 °C


Suitable forBosch, Siemens, Denso and Delphi CR systems


Carrying case 
Hose plugs10
Hose clamps5
T coupling1
I coupling1

The Diesel Return Flow Sensor RFS400 is delivered with:

1 Diesel Return Flow Sensor RFS400
10 Hose plugs
5 Caps
5 Hose clamps
1 T coupling
1 I coupling
  various adapters to connect to most common injection systems
1 Carry case


Diesel return flow measurement

With a lab scope and an Diesel Return Flow Sensor RFS400 the return flow from common rail diesel injectors is measured. The signals from the Diesel Return Flow Sensor RFS400 are shown and can be downloaded. To help determining whether the injectors are functioning correctly, different deviations from the example signal are mentioned along with possible causes.
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Exhausted Mercedes E-class

A Mercedes E-class was hard to start, flattened the battery and left the owner stranded. The first garage is was sent to concluded that the immobilizer ECU had forgotten the key codes. The vehicle was then sent to a garage with AECS technical support and using an automotive diagnostic oscilloscope and RFS400 return flow sensor the found the real cause of the problem.
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