Cummins Engine Repair- ISC Engine Code 434

Cummins Engine Repair not only involves mechanical but electronic repairs as well. The ISC model has an ECM that sends and receives messages that controls every performance aspect of this engine. The main source of power is the battery that depends on wiring that feeds the Cummins ECM sufficient voltage to run the engine systems.
Pictured is the laptop shot of an active code #434 a power interruption that derated the engine to a crawl. Derating protects the engine from sustaining high speeds and rpms which would cause more severe damage. This ISC Cummins Engine is in a 1999 Thomas School Bus Saf-T-Liner. With an active code you can retrieve it with the diagnostics switch [on the dash] & ignition switch turned on. The code will beep each number with a pause, in this case 4 beeps 3 beeps 4 beeps with a pause in between each #.

A closer look [click on photo to enlarge] shows numerous fuses on the positive feed wire to the Engine ECM [electronic control module]. Our code information is telling me there is a power problem so "the first thing to check is the Source."

Using a digital ohmmeter check the fuses for continuity and clean all the connections.

Note: Before this maintenance step I could not get a reading on my laptop, there was a communication error between the engine and the "Cummins Insite" software.
After cleaning all the connections and testing the batteries the communication problem was erased and the code disappeared.

There is a variety of 7.5 and 10 amp fuses inline with battery to ECU supply power. I traced the wiring back along the frame as well to check out any other possible problems. The rule of thumb in this situation is to check connections and wiring closest to the environment and work your way up the line.

Using a Snap-On Micro Vat Battery Tester I concluded that all the batteries were in good condition. This tester does a very quick assessment of battery condition and also tests starting and charging systems quickly.

The Conclusion to this problem was simple, servicing the battery connections which had enough resistance to cause the #434 code to occur. It makes sense since the ECM reads Voltage at a very sensitive level.

After an extensive road test the code did not come back and this experience was a good one telling me [and you the reader] to always check the simple things first!

Now we're ready for the next challenge with Cummins Engine Repair.

Recommended: Diesel Engine Repair Manuals

Allison Automatic Transmission Wiring & Troubleshooting

The Allison Transmission Control Unit on the 1999 Saf-T-Liner is located under the floor directly below the driver. There are 3 plug-ins which is an easy way to tell this is a W-TEC 3 system [World Transmission Electronic Unit 3rd generation]. The Transmission vehicle speed signal enters here and exits at two different plugs, one for the speedometer and the other to the Cummins ISC ECU.



We will trace the exiting wire from the ECU that provides our Vehicle Speed Signal since that is the code and the speedometer is operating normally. Since we have speedo operation that gives us an obvious clue that the incoming signal to the Trans ECU is OK.[resistance should be checked regardless]
The wire we want to trace goes from the Trans ECU to the VIM [Vehicle Interface Module]
Removing the dash back cover makes this check MUCH easier.


Remove the cover from the VIM








The VIM is an interface between the Trans ECU and the chasis wiring. Various operations are accomplished through this module like the exhaust brake, back up lights, neutral start, high idle and of course our vehicle speed signal runs through here to the Engine ECU.
[Click the Pic to Enlarge]
Now we can check the continuity and see if we have a circuit. After checking this out there is no connection between the Trans. ECU and the VIM.
I'll run a new wire to repair the open circuit, an easy fix. It's nice to get a gimme once in awhile!

In the VIM you'll notice a series of relays and 2 fuses. If you experience a dead keypad and there is battery voltage to the VIM then check these fuses. One is main power & the other is ignition power.



The other vehicle speed signal wire [tan wire # 157] comes from the trans ECU directly to the speedo. The speed signal to the VIM is the same number [tan wire #157] since it comes from a different plug.




This is where it all begins from the output shaft housing of the transmission. The output sensor is a single coil unit that sends an AC voltage to the Trans ECU.
There is a toothed wheel rotating inside the housing that creates the signal to the sensor.
The Allison 3000 Automatic Transmission is a very reliable unit when maintained properly. The wiring problems come and go but are easy to trace and repair with the right tools and wiring diagrams.

Cummins ISC Electronic Diesel Engine- cranks over but will not run.

Cummins ISC Diesel Engines need to be analyzed using a laptop computer with Cummins Insite software.

Sometimes however you can troubleshoot a no run problem the good old fashioned way by looking listening and using common sense.

The fuel transfer pump mounted on the left rear of the engine is a vane type unit driven by an electric motor.

The first clue was the transfer pump motor was not running at all with the ignition key on, it will charge up the system every time you hit the ignition key with a very distinctive motor noise at high rpms.

So since the golden rule with electrical problems is to check the source I went to the battery and checked the multiple fuses that supply power to the engine ECU [electronic control unit]

I found 3 fuses had blown indicating a possible short or high amp draw. The first thing to do was hook up a jumper wire [with an inline breaker in case there was a short]

Once hooked up the fuel transfer pump started working but sounded very sickly! It was enough to limp the School Bus back to the shop.

Since the main problem was a overly high draw from a faulty fuel
pump motor, replacing the fuel transfer pump was our next step.

The fuel pump must be installed as a unit [do not just change pump and motor] and will not seal properly on the old housing. You are guaranteed to have a fuel leak once you start it up.

How do I know? because I tried it as a shortcut and instantly had a fuel leak between the housing and fuel pump/electric motor.

There is very little room to move in this Thomas pusher since it is a rear engine unit. Remove power steering lines and rear radiator frame brace to gain access to the pump housing fuel lines and mounting bolts.

Test the pump by cycling it a few times with the ignition switch.

Fuel filter replacement is recommended, we pre-fill the primary filter and install the secondary filter dry which allows incoming fuel to be pre-filtered instead of being poured out of a fuel container, this avoids contamination.

The new fuel transfer pump will do all the work priming the system.

Just listening to the uncharacteristic sound of the fuel transfer pump led us to this rather easy diagnosis. It's a gimme that doesn't happen too often.

The main tip here is to always check the source first when troubleshooting a problem. Electronic diesel engines like this Cummins ISC model still run off a 12 volt battery so things have not changed too much from a few decades ago!

School Bus Mechanic on my "Squidoo" Lens