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Cat Man
Cat Man, Cat Engine Expert
Category: Medium and Heavy Trucks
Satisfied Customers: 8812
Experience:  I am ASE Master Truck Certified.
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I have a 1999 peterbilt with a 3406e model 2ws serial #

Customer Question

hi
I have a 1999 peterbilt with a 3406e model 2ws serial # ***** in it. I have a engine fan problem. Fan stays on all the time. In cab switch does not work either way on auto or manual. when checking the switch I have power to it and when you flip the switch you get power coming back out of switch but I never get power back up to the solenoid. Solenoid is new. if I hard line route air to the fan it will go on and off. I also have some issues with the motor running rough and vibrating , pour acceleration, low turbo boost. water is clean and motor burns no oil. have put a ton of new parts into it and still baffled. could it be the ECM?
Submitted: 1 year ago.
Category: Medium and Heavy Trucks
Expert:  Cat Man replied 1 year ago.

Thanks for asking your question. I will try and help you out.

Yes it's possible to have a faulty ECM. But often a bad ECM is not the problem.

The ECM will turn on the cooling fan, if any of the following conditions are detected by the Engine ECM:
The engine coolant temperature is greater than 102 °C (216 °F).
There is an active diagnostic code for the coolant temperature sensor.
There is an active diagnostic code for the intake manifold air temperature sensor and boost pressure is greater than 70 kPa (10 psi).
The intake manifold air temperature is greater than 87 °C (189 °F).
The intake manifold air temperature is greater than 72 °C (162 °F) while the boost pressure is greater than 70 kPa (10 psi).
The "Fan with Engine Retarder in High Mode" is programmed to "YES" and the retarder has been on at least two seconds.
The "A/C Switch Fan On-Time" is programmed to a value above 0 and the A/C high pressure switch is Open.
The manual fan override switch is on.
If you do not notice any of these conditions occurring, one of the items above may be faulty and causing the fan to stay on. For example, you could have a faulty AC high pressure switch, manual over ride switch, or the wiring to one of these items could also be faulty. The tough part is if one of these is faulty, there will not be a check engine light or fault code.

The best way to determine what is causing the engine fan to stay on is to connect a service tool like Cat ET software and monitor the fan and all of the switches that are connected to it. If one of the above is keeping the fan on, it will be easy to see. For example, if you have a bad AC high pressure switch, it will say that the AC switch is wanting the fan on.

If nothing can be seen with the service tool, you most likely have a faulty fan control solenoid, fan hub, or broken fan control wire that runs from the engine ECM. It is on pin 11. Basically, the ECM sends out 12 volts on pin 11 whenever the ECM wants the fan off. When the ECM wants the fan on, it removes the 12 volts from pin 11.

If your fan is on and you have NO POWER coming out of pin 11, one of the items I first mentioned is making the ECM want to keep the fan ON.

If your fan is on and you have POWER coming out of pin 11, you have a faulty fan control solenoid, fan hub, or broken fan control wire.

Please reply back if you need more help or have more questions. I am happy to assist.

Customer: replied 1 year ago.
cat has hooked it up to ecm 4 times to try to figure it out. does not throw a code of any kind. has farely new fan hub that works just fine if I hard line route it to a air switch. solenoid is brand new and switch in cab has been changed and still no change. I do not get any power to solenoid. I still have the problem with the motor running rough vibrating like the timing is advancing or retarding and loss of turbo boost. which is why I was asking ecm?
Customer: replied 1 year ago.
also fan is not to have anything to do with jake brake of cruse control as set in ecm.
Expert:  Cat Man replied 1 year ago.

Thanks for the information.

It is very possible it's the ECM. It's rare but I see it from time to time.

The ECM sends out 12 volts to turn the fan off. When it wants the fan on it removes power. If it takes power to turn the fan on. The. Your truck has a relay between the pin 11 ECM wire and fan solenoid. I would make sure the relay is OK. If the relay is good. The only way to verify a bad ECM is to install a known good ECM.

As far as the low boost and vibrating. I would check the fuel pressure. If it is low there will be no codes. Your engine should maintain a fuel pressure between 75 and 90 psi. There is a plug beside of the secondary fuel filter that is used to check the pressure. If it is low, I would first try the fuel filters if you haven’t already. If it is still low, you may have a failed fuel pressure regulator, which is located underneath the bottom of the filter housing. I have replaced a ton of these for low fuel pressure. It is kinda a known problem. You could also have a weak fuel transfer pump or restricted hand primer pump, if your engine has one.

Please reply back if you need more help or have more questions. I am happy to assist.

Customer: replied 1 year ago.
I have a brand new wiring harness from firewall of truck to ecm and that is where the wire comes out for the fan solenoid. I see no relay in that wire. is there another location it could be? fuel pressure checked to 85 psi and has new fuel pump and fuel lines.
Expert:  Cat Man replied 1 year ago.

The relay is normally on the fire wall or near it.

If it takes power to engage the fan there is either a relay or the fan solenoid is the wrong one. Normally if there is a relay you can flow the wires from the fan solenoid and it will lead you to it.

Customer: replied 1 year ago.
the wires from the solenoid go directly into the harness that go to ecm. 2 wires and there is no relay in it. the solenoid looks just like the one that was on it before and got it from Peterbilt off of the vin # ***** truck.
Expert:  Cat Man replied 1 year ago.

A power to engage fan solenoid and a power to disengage fan solenoid look the same. It could be the wrong one.

When the fan is on I would check for power on pin 11 of the ECM. If you have power on pin 11. The fan should be off. If it is not. It's either a bad fan solenoid, bad relay(if there was one), or a broken wire from pin 11, or a bad fan hub.

Expert:  Cat Man replied 1 year ago.

Hey. I just wanted to see how things were going. Please let me know if you need more help. I am happy to assist. If my information was helpful, please leave a good or higher rating so that I receive credit. Thanks.

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