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 Pre Heater on C7 Cat
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eshover
Senior Member

146 Posts

Posted - 03/31/2014 :  06:02:55 AM  Show Profile  Visit eshover's Homepage  Reply with Quote
I've got a '06 AA with C7 Cat engine and the "Wait to start" light comes on on gauge test but will not stay on when it should be pre heating.
Anyone know how to check to see if it's the heater grid or something else?
Thanks,
ED

Thomasbus24
Administrator

USA
4544 Posts

Posted - 03/31/2014 :  1:50:17 PM  Show Profile  Reply with Quote
WOW...I was just going to post this exact same thing....same bus, year and all.

Hope we get some good info!
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aaronwilmoth80911
Top Member

538 Posts

Posted - 04/01/2014 :  06:14:43 AM  Show Profile  Visit aaronwilmoth80911's Homepage  Reply with Quote
Maybe try to see if you can find a Ohms specification for the grid and check the Ohms on it. Also maybe check to see if there is voltage going to the grid when you turn the key to the on position. This will probably require an extra set of hands, but may get you on the right track as to where to go next. Good luck!
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tigger2
Advanced Member

USA
469 Posts

Posted - 04/01/2014 :  10:37:06 AM  Show Profile  Click to see tigger2's MSN Messenger address  Reply with Quote
If there is a low current problem in the relay or the heater the Cat ECM should set a fault code. Look in the events section of the diagnostic software, useually follows active codes, logged codes and then logged events. Logged events often are the most helpfull.
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bwest
Administrator

United States
3820 Posts

Posted - 04/02/2014 :  09:30:35 AM  Show Profile  Reply with Quote
quote:
Originally posted by tigger2

If there is a low current problem in the relay or the heater the Cat ECM should set a fault code. Look in the events section of the diagnostic software, useually follows active codes, logged codes and then logged events. Logged events often are the most helpfull.



Check the connections at the relay too. I've seen them get hot and loose connection.

Bryan
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eshover
Senior Member

146 Posts

Posted - 04/07/2014 :  10:13:54 AM  Show Profile  Visit eshover's Homepage  Reply with Quote
I haven't had a chance to diagnose this yet but another AA had the power terminal actually get hot enough to melt the plastic around the terminal on the heater solenoid and cause the "Warn Engine" and alarm to come on and stay on. Replaced the solenoid and took care of the problem. It's not cold enough now to make heater come on so I don't know if I can check anything now.
ED
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Cal Mc
Advanced Member

303 Posts

Posted - 04/07/2014 :  11:02:36 AM  Show Profile  Visit Cal Mc's Homepage  Reply with Quote
I have never seen a fault code set for heater relay or grid not working. Most failures are usually the heater relay. We have been replacing them with the silver coloured "WHITE ROGERS" relay from Blue Bird. They are a little bit larger but more durable and half the cost.
When you turn on the key and the "intake heater" light or "wait to start"light comes on, the voltage gauge will read below 12V. as soon as the light goes out the voltage will climb to battery voltage. During cold weather the intake heater will come back on after start-up. The voltage at this time may also read lower than normal until the heater goes out. If your intake heater light is on and the voltage is not low, it is a fair indicator of a heater circuit failure.
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Cal Mc
Advanced Member

303 Posts

Posted - 04/07/2014 :  11:28:49 AM  Show Profile  Visit Cal Mc's Homepage  Reply with Quote
Almost forgot, we have had some issues with temp sensors, coolant and air. The Cat ecm uses a combined reading of the two sensors for activation of the intake heater relay. Our Cat C7 engines use the same part number in both locations.
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eshover
Senior Member

146 Posts

Posted - 04/14/2014 :  07:30:43 AM  Show Profile  Visit eshover's Homepage  Reply with Quote
I replaced the heater solenoid right next to the heater because its input terminal had been very hot. Did not fix the problem.
Where is the heater relay you spoke of?
ED
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bwest
Administrator

United States
3820 Posts

Posted - 04/14/2014 :  10:59:52 AM  Show Profile  Reply with Quote
quote:
Originally posted by eshover

I replaced the heater solenoid right next to the heater because its input terminal had been very hot. Did not fix the problem.
Where is the heater relay you spoke of?
ED



You just replaced what I am calling a relay. I should change my lexicon I guess. Solenoid, Relay, same concept different parts I guess. lol This might be a dumb question but did you check for power coming into that solenoid? Also did you check signal power and signal ground. Hope I'm not talking some southern Illinois slang that no one can understand. lol

Bryan
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eshover
Senior Member

146 Posts

Posted - 04/14/2014 :  1:39:10 PM  Show Profile  Visit eshover's Homepage  Reply with Quote
I just checked voltage at input terminal and it is battery volts. Checked both of the small terminals and they both have at least 12 volts.
Checked the rear output terminal and it has almost 12 volts when key is turned on then goes to 0 in a second or two. The wait to start light is still on in the gauge check mode when this happens. No matter how cold it is (36 degrees right now) the wait to start light will not come on after the gauge check mode.
I'm not sure what the signal ground is.
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bwest
Administrator

United States
3820 Posts

Posted - 04/15/2014 :  05:31:37 AM  Show Profile  Reply with Quote
Well, I was thinking there has to be a ground on the other side of the coil that activates the solenoid but it might go through the case. If you're getting power for a few seconds on the output I would think all is well at that point. You need to look at the sensors now, in my opinion.

Bryan
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tigger2
Advanced Member

USA
469 Posts

Posted - 04/15/2014 :  06:30:07 AM  Show Profile  Click to see tigger2's MSN Messenger address  Reply with Quote
The intake heater solenoid is ground controlled from the ECM. The power supply for the relay , heater and lamp are OEM. Check the ground strap at the rear of the cylinder head to ECM. The output wire is in pin 8 in connector 1 at ECM this is the engine side.
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08 Thomas EF
Top Member

533 Posts

Posted - 05/26/2014 :  09:40:35 AM  Show Profile  Visit 08 Thomas EF's Homepage  Reply with Quote
Eshover, just curious if you were able to figure this out.

Edited by - 08 Thomas EF on 05/26/2014 09:40:52 AM
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eshover
Senior Member

146 Posts

Posted - 05/28/2014 :  1:17:42 PM  Show Profile  Visit eshover's Homepage  Reply with Quote
I never got back to it to check anymore. It got warmer so didn't need the pre heater. I will probably take it to CAT this summer as I have done about all I can do to diagnose it. They said they can check it even though it is warm weather.
I will let you know how I come out.
ED
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offroadwolf1
Active Member

33 Posts

Posted - 06/02/2014 :  11:13:18 AM  Show Profile  Reply with Quote
I just saw this thread and it mught be a dead issue. But here is how the dealer tests the grid heater in the summer. If you have CAT ET on a laptop you have the ability for a special test to activate the grid heater. Once you go in and and activate the grid heater go check the intake air tempeture. The intake air temp will increase while you have the grid heater on. I don't ever run them longer then 30 seconds at a time and make sure you give it plenty of cool down time. This way you can verify the grid heater is funtioning.
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eshover
Senior Member

146 Posts

Posted - 06/03/2014 :  07:15:16 AM  Show Profile  Visit eshover's Homepage  Reply with Quote
I don't have a laptop or program to check it with. I wish I did but we are too small to use one alot.
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g0ttadrift
Advanced Member

USA
258 Posts

Posted - 01/29/2021 :  1:48:01 PM  Show Profile  Reply with Quote
Hey eshover, I know this was from 6 years ago, but the system throughout the new buses have stayed pretty much the same. Were you ever able to take it to CAT and what did they find? Thanks.
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