On most new diesel engines, a strategy to comply with pollution mitigation requirements is to recirculate the exhaust gasses back into the cylinder. To do this, an electrically controlled valve is needed to open and close to create this circulation path. Since this is an important feature, the engineers who programmed and specified the fault code requirements for the exhaust gas recirculation (EGR) valve made it so the EGR needs to be tested upon key-on. If the dynamic signals from the EGR are not present upon startup, then a new fault code will be set. If a goal is to have a fault free system, then this is a critical signal to simulate.
The Fault Code
As an example, we will look at Cummins Insite to see what fault codes are present when an EGR is missing.
If you double click on this fault code, it basically says the ERG is missing or doesn’t work. Another piece of information that is useful can be obtained from the wiring diagrams on Cummins Quickserve Online (qsol.cummins.com).
The EGR Schematic
This schematic information says there are 8 pins, which are labeled in a different section of the same schematic.
Connecting the EGR on the Bench
Connect Pin1 of the EGR (gray/blue in the photo) to a 5V supply, or Pin J1:81 in a Cummins CM2350 engine control module.
Connect Pin2 of the EGR (gray/black in the photo) to ground or return, which is pin J1:57.
The smartest thing to do is to buy a a matching connector, but the part AMP or TE or whatever part number isn’t available from Cummins, which means you would have to buy their part to figure it out. Sometimes the connectors aren’t available separate from the harness, which is really expensive. So, the next best approach is to pin out the connetor with test leads. To build the test leads, we used the following:
- 20 gauge GLX wire, two wires per connection. One wire is for the ECM and the other is for the test leads from the oscilloscope.
- Heatshrink. Our favorite is the Qualtek Q5-3X-RK1-1/4-01. It is an adhesive lined semi-ridged heatshrink for automotive purposes.
- The terminals use for this connetion were some old Junction Timer terminals for 2.8mm blades. Something like these should work: http://www.mouser.com/ProductDetail/TE-Connectivity/927774-3
A couple photos of the test leads show how the heatshrink can be used to insulate the pins and terminals from bumping each other during the tests.
EGR Pin, Color, Signal, CM2350 Pin
1, Gray/Blue, +5VDC, J2:81
2, Orange, Position A, J2:47
3, Yellow, Position B, J2:46
4, Pink, Position C, J2:22
5, Gray/Black, Ground, J2:57
6, Gray, Motor B, J2:24
7, Green, Motor C, J2:48
8, Blue, Motor A, J2:23
Once the test lead connections are made with the EGR, the ECU needs to see them along with the Oscilloscope. The signals generated from the EGR valve are 5 volt digital signals that reflect one of three positions of the rotor of the brushless DC motor. These are typically called hall effect outputs. The transitions on channel B occur about 1/3 of the pulse width after the transition of channel A. Channel C transitions happens about 2/3 of the way through channel A.
With these signals connected to the ECM, the fault code for the sensor is cleared or shown to be inactive, but the fault code for the EGR Valve Control Circuit – Current Below Normal or Open Circuit is still present.
A good reference for further reading is http://www.mouser.com/pdfdocs/BrushlessDCBLDCMotorFundamentals.pdf
Simulating the Presence of a EGR Valve
We seek to produce a low cost replacement for the EGR valve that can be used to simulate the presence of the EGR for the engine control module. To this end we introduce a new idea called the Smart Actuator Simulator