2002 kenworth with a CAT 3126 engine- crank no start. I am looking for schematics for engine and OEM side as well.

Hello and welcome to JustAnswer! I'm Nick and I'll be helping you out today. I'll be back within 30 minutes with some diagrams for you.

No problem. I'm working on this now.

Here's the Cat diagram.

Here's one KW harness.

Here's another KW diagram.

Both of those diagrams came up under OEM engine harness.

No, sorry. I'm more familiar with HD engines. I will see if I can get some more specific information for you from Caterpillar.

Ok, so it looks like the control valve will only have current when running or cranking. It's job is actually to bleed excess oil pressure. Try unplugging the injection actuation pressure sensor and cranking the engine. It's on the top driver side of the engine near the front.

Do you have Cat software?

Ok, I'll make a document together this evening and send it to you.

No problem.

Here's an overview of reasons why the engine may not start. I'd start by monitoring engine speed/timing sensors with CatET. Then check the power, ground and ignition supply to the ECM. Make sure the voltage doesn't drop too much while cranking. Make sure the batteries are in good condition and the cables are clean, tighten and corrosion free. Remove the rear ECM plug and check for corrosion or damaged wiring. From there move on to monitoring the injection actuation pressure as the document suggests. After all of that is verified I'd move on to fuel system checks. I'll send some separate documents for checking the timing sensors, power supply circuits and fuel system if necessary.

Here's the speed sensor troubleshooting. The illustrations are missing, but use the Cat wiring diagram if you need to check wiring.

Here's the ECM power supply information. Use the KW diagrams if necessary.

Here's information on the fuel supply pressure.

It's very likely that you have a failed high pressure pump. If the fuel supply is good, but the injection actuation pressure is low you'll need to replace the pump. If the pump has failed you should replace all 6 injectors also. There are large plugs on the front and back of the cylinder head where the high oil pressure rail is. If the pump has failed use a telescoping magnet and check the rail for metal shavings.

No problem. Let me know what you find or if you need further assistance.

Ok, with the 6 injector current faults the issue is going to be the ECM. But give me just a minute to pull up that 8 voltage supply shorted low. I'm not too sure if that would be related.

Yes, the inactive injector faults are common for an ECM failure in any Cat engine. Most of the time they are inactive. If I see that I'm automatically replacing the ECM. No checking or troubleshooting anything.

The 41-4, 8 volt supply, is the supply for the throttle position sensor only. If you have disconnected the throttle or disconnected the ECM connector with the key on I would ignore it.

The 42-11 and 164-11 could be anything from a plugged fuel filter or an issue with the fuel pump. Once you get the engine running you can perform some tests on the fuel system.

Ok, I'll send the troubleshooting for the sensor supply fault. It may be the ECM causing that too though.

Right, it would cause the throttle not to work. It wouldn't cause it to not start.

Yes, that may indicate a weak pump. Make sure the oil is in good condition. If it's degraded it won't be able to raise the pressure easily.

No, it wouldn't.

No problem.