1998 Patriot Crank/No Start

[Bill Drout]

My 98 Patriot cranks but will not start.  My suspicion is that it's a failed CAT ECM, but I'm trying to follow the correct diagnostic procedure before condemning the ECM. 

This post was very helpful:
http://beaveramb.org/forum/index.php/topic,6777.0.html

Here are some symptoms and/or data points:
1) When the ignition is switched on, the Allison shift pad lights up. 
2) No check engine light.  If I hold down the resume button for 20 seconds, I do not get the 55 flash code (or any other flash code). 
3) If I turn the key to on, the speedometer test cycles but the tachometer does not.  It's my recollection that they both used to test cycle. 
4) I do not get a tach response when I crank the engine.  I would expect it to jump to 200 or so.  The needle appears to actually drop below zero on crank.
5) I used to get a light for the heated air inlet, and I would wait until that goes off before starting the engine.  But that light no longer comes on.
6) Engine Warning light illuminates when the ignition is switched on, but I believe this is normal.
7) And the obvious: Engine cranks fine but does not start.  It's not an intermittent start.  It won't start at all.

Other data:
1) The two 10A fuses in the Allison VIM box are good and are getting power.
2) CB21 (Ignition Power Relay) and CB22 (Ignition Service Board Transmission) appear to be good.  I understand from the post above that they could be intermittently failing, but my symptom is a "no-start" and not a "sometimes no-start". 
3) The Bosch relay back at the battery bay is good.  I'm thinking the relay is the "ECMR" (ECM Relay).  There's a sticker in the battery bay which bears little resemblance to the actual wiring back there, but it has a picture of a relay pinout labeled "ECMR".  I'm pretty sure that's what it is.  I'm guessing the pick wire going to relay pin 85 is ultimately coming from CB21 in the front electrical bay.  I'm also guessing that the Normally Open (NO - relay pin 87) is going to the J1 pin 70 of the Cat ECM.  But I'd like to verify that.

Does anyone have the wiring diagrams for a 1998 Patriot?

I have been looking at the diagrams for the 1996 Patriot on a Magnum chassis in Coach Assist, but those schematics are for the CAT 3126, and the 98 Patriots have the CAT 3126B.  That's relevant because CAT changed to the ADEM III ECM on the 3126B in 98.  That ECM has two 70-pin connectors with different pinouts from the previous model.  I can find some generic pinouts from CAT for "typical" connections, but I'd prefer to see the actual diagrams for this coach. 

My next approach is to pull the J1 connector on the ECM and test for switched power on pin 70, constant power on pins 52 and 53, and a good ground on pins 65 and 67.  If all of those check out, is that sufficient to make the call on a bad ECM, or do I need to check for something else first?

Any assistance or advise would be greatly appreciated.

[Eric Maclean]

Bill
The relay you're talking about is the ECM relay and it provides power to the ECM upstream of that relay there should be a small ATO style in line fuse holder with a 20 amp fuse in it which provides the ECM power that fuse holder should be somewhere between the batteries usually directly connected to the batteries and the relay if that fuse is blown there's no ECM power.
The relay itself is controlled by the service panel switch a loss of power to the panel or bad switch may cause the ECM relay to not function also check the ground for the ECM relay.
I personally had a problem with the service bay switch on my coach it became intermittent and would not switch back and forth probably due to corrosion caused by debris thrown by the back rear wheels up into the service panelI have since installed a mud flap to stop the dirt and debris from being sprayed up there from rear wheels.
The dash ignition switches are also known to go bad.

You're going to need a good wiring diagram for the 3126b you need to be checking both power feed and grounds they'll be fed to the processor through a twisted pair.
If you are correct there is no power to the ECM at this point plugging a scan tool in will give you no communication the scan tool also picks up its power from the diagnostic plug which is fed by the ECM power along with the J1708 protocol.
AsI have stated in previous posts ECMs very seldom fail on their own, there are rare cases but usually they are murdered meaning and outside force like a voltage Spike reverse polarity shorted wiring etc kills the  ECM .
It's been my experience many ecms have been replaced for no apparent reason the later cause usually found to be poor wiring or bad connection usually on the bodybuilders side cat as well as most OEM engine production people do a pretty good job on their own wiring harnesses but they cannot control what's the bodybuilder puts in, that would he where I would where I would concentrate my efforts.
Dave Atherton may be able to help you out with an accurate wiring diagram for your 3126B  to help pin out the ECM wiring ,as for the coach builder side I would believe that the 1996 Patriot wiring diagram should be fairly close as Beaver didn't like to change things much from year to year
Hope this helps some feel free to ask any questions you like.
Good luck
Eric

[Steve Huber Co-Admin]

Bill,
Since your coach has the Magnum chassis, most of the early e.g.  1997-2004 coaches using the 3126B should have the same or very close wiring.  The 2002 Patriot had a 3126B but the 03 had a Cummins. Both are covered in one set of dwgs in CA.
Steve

[Gene Obie]

Diesel Engine Trader has a forum post with similar CAT ECM problem (different CAT engine). He solved the no start/no check engine light by basically resetting the ECM. He pulled all power to ECM for a few minutes and reconnected (had to do it several times for some reason). I think you actually have to pull chassis battery cable since ECM is power is tapped off before any isolation switch.

[Steve Huber Co-Admin]

All,
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[Bill Drout]

Many thanks to the input I've received from everyone. 

My coach has the Racor fuel/air separator for the fuel system.  I ran the air purge and it looks good to me, so I don't think that it's an issue with air in the fuel line.  I understand that this is not a definitive check of the fuel system, but it does appear normal to that point.

Given the way the problem developed and the new information received from the testing I've conducted, I'm really starting to think it's the ECU. 

The IntelliDrive module gets no sensor data from the ECU, but it's getting data from the Allison transmission just fine.  Values such as air inlet temperature, coolant temperature, and battery voltage show zero values on the IntelliDrive while transmission temperature shows to be normal.

As previously mentioned the speedometer test cycled when switched to the IGN key position, but the tachometer does not.  The shift tower lights up and show "N".

I pulled the J1 connector from the ECU and tested for voltage and grounds.  Pins 52 and 53 show constant 12V.  Pins 65 and 67 show a good ground.  Pin 70 shows a good switched (IGN) power.

With the J1 connector removed from the ECU, I'm getting exactly the same behavior (no data to Intellidrive, tach dead) as when the J1 connector is attached. 

There's a shop in Fort Worth that will repair a CAT ECU for substantially less than what I would have to pay to get one from CAT.  They say they can fix most ECU's, and there's no charge if they cannot.  The service charge is $129 if they find nothing wrong with the ECU.  I'm thinking that's the way to go as long as I can get the ECU out of the coach -- which is not a trivial task given all of the stuff surrounding it.  I'll let you know how it goes.

Thanks again for your help!!

[William Theriot]

Bill, I had the same problem with the switch in the service compartment. Shut me down completely.

[Bill Drout]

Hi William,
  Did you also have power going to the ECM and no data being received from it at the front of the coach?  That's what has got me thinking that it is the ECM and not some external electrical or fuel issue.  The ECM definitely has good power and grounds on the pins that, according to my research, should have power and grounds.

  On my coach I have an engine start and stop button in the service station, but I don't have a switch like a key switch.  I also don't have a battery disconnect switch for the chassis batteries.  I have always thought that to be strange.  It may have been there originally, but it was gone by the time I bought the coach.  And it was probably not in the service station since that area appears to be original.

  The reason why I'm asking is that I've got the ECM out of the coach and ready to send in for diagnosis.  If you had the exact behavior then maybe I have a flaw in my reasoning.

Hi Eric,
  Do you have a recommendation on a scan tool to use for communicating with the ECM?  I hear what you are saying about making a premature call on a bad ECM.  I'm thinking that a bad switch in the service bay of the coach would keep power from getting to one of the pins (probably switched power on pin 70), and I'm seeing power everywhere I would expect power. 

  Also I have a theory on why the ECM may have failed.  My batteries have been weak, and I've been putting off replacing them because I need to take the coach in for service that was unrelated to this issue.  It's been my experience that shops are notorious for leaving stuff on and and flattening batteries.  Then they recharge them and don't tell you, and you only find out about it 2 months down the road when the batteries fail on you.  I was putting off replacing the batteries until I got the coach back from the shop because I didn't want to risk flattening a brand-new set of batteries.  During my research on this issue I've discovered that low voltage, or voltage spikes (perhaps from using the boost switch) are pretty hard on these ECM's.  It's just a theory, but that's my thinking on why the ECM died.

Hi Gene,
  I also took in to consideration what you mentioned about disconnecting the chasses batteries.  I have done that several times just in the course of diagnosing.  I even disconnected all positive and negative wires from the chassis battery and touched them together in case I need to discharge a capacitor somewhere.   

Thanks again for everyone's input!

[Fred Brooks]

  Bill, Does your coach have a "rear run and start switch"? From following this tread it sounds like a 22 year old switch in a hostile environment could be the culprit. The switch center pin or connection is the output, bottom pin is the ignition power from the front when the key is on, and the top pin is 12 volt chassis power from the rear. (I may have that info transposed) Please advise, Fred

[Bill Drout]

Hi Fred,
  I do have a green start and a red stop button in the service center at the back of the coach.  I'm guessing this affects power to to the ECU.  Does anyone know how? 

  I see the wiring diagrams for the Patriot 2002-2003.  The closest thing I see is drawing 38030067 with the title "C12 Engine Harness - No Serv Center".  Mine is a 3126B with a service center from 4 years earlier, so it's not the best overlap.  However it does show the CECM connector which would be to a dual 70-pin ADEM III ECM like mine.  The "CECM (Engine Connector)" table on drawing page 2 of 2 does show the wiring harness with pins 52 and 53 getting constant 12V.  It shows pins 65 and 67 connected to chassis ground, and it shows pin 70 to switched IGN power.  All other pins are for communication in some form.  All of this corresponds to the best information I have on my coach, and it matches the actual measurements of the J1 harness on the coach.  Still crank but no start, a dead tach, no check engine light, and no ECM communication to the Intellidrive.

That's why I'm thinking it's a dead ECM.

[William Theriot]

Bill,  My unit was running fine when I killed it at the campground. Four days later, nothing.  Crank and crank but no start.  On my 98 tourmaline , there is a 3 way toggle switch in the service bay for front start, off, and rear start. My mechanic connected a lap top to a port in the service bay and found there was no power to the ECM. He then traced the problem to the switch in the service bay. He then bypassed the switch and bingo, back on the road.  I hope this helps.

[Carl Boger]

Bill I am by far no expert, but if you have power to your ecm then I doubt that your rear start switch is the problem.
 As far as the battery cut off switches, my coach does not have them either, and never has.  I am in the process of adding them when I get a day off with good weather.  It is one of those really not needed but I want it options

[Eric Maclean]

Bill
As for scan tools the best you will get for your Cat engine is the Cat software as none of the other aftermarket units will give you as much access to the systems or function test ability as the Cat unit .
That said I've used J pro software to access mine and it did what I needed to do but it's also a very expensive commercial  scan tool and if all your going to use it on is your Cat engine the Cat tool would be the tool of choice.
As Dave points out a full access commercial scan tool can be a dangerous thing in the wrong hands I've seen more than one ECM with bad or no programing left after a botched reprogram by someone who didn't know what they where doing .

The switch I spoke of earlier is the same toggle switch referenced in the last post it controls the ECM relay located in the top left side of your battery bay it basically switch's the ignition feed signal from the driver's station ( ignition switch) to the service bay switches. most busses are set up this way so you can kill the driver's station controls when you are working on the engine for safety reasons.
The relay switches circuit # 201 which is the ignition power to pin #70 on your CECM.assuming yours is as you say a CECM
That switch has a bad habit of having poor or no connection inside usually because of corrosion and age or inactivity.
If the coach was just in for service there is a good chance the tech may have used that switch at some point and now  it's starting to give you problems.

How ever you say with the ECM out of the coach and the ignition on  you have  12 volts + at pin #70 ignition power feed this is the wire which comes from the ECM relay known as circuit #201
You should also have 12 volts + on pin numbers 52 and 53 these are battery power feeds.
Don't forget to check the grounds to the ECM as well those should be pins number 67 and 65.

If you are certain that you have all of the above and still get no communication from the ECM then it would be time to sent the ECM out to be checked.
If the ECM is not powering up it will be doubtful that you will see any communication with a scan tool or anything else connected to the data buss like your silver leaf or Magnum inteldrive system.
I have seen processors killed by overzealous battery chargers but usually there done right there on the spot , most natural ECM failures are thermal cycle related the others are as I said in an earlier post they are murdered.
The engine builders like to mount the ECMs to the side of the engines to ensure they kept there wiring to a minimum and this gives them control over there side of the wiring but at the same time it exposes the ECM to the there so cycling of the hot engine.

The 1996 Patriot wiring diagrams show the ECM relay wiring on page 18 the pin out at the ECM may be different with the CECM configuration but the circuit should work the same way.

Hope this helps
Eric

[Bill Drout]

I decided to go ahead and ship the ECM off to 1EngineControl in Fort Worth.  I requested a tech report on the ECM which should give us a good idea of what failed on the ECM.  If I'm wrong (not a bad ECM) then the diagnostic fee is $150.  That's still worth it to me at this point in time.   I'll let you know what they determine. 

This thread had a lot of discussion about the service bay configuration.  In case anyone else finds this thread and is interested, attached is what the the 98 Patriot service bay looks like - including the "Engine start" and "Engine stop" buttons.  During troubleshooting I tried to start from the back (with the IGN switch on) with no success. 

To the extent it's helpful, I can give some ECM details for anyone else that may go down this path.  The ECM is secured to the engine underneath the intake manifold by four 13mm bolts on stand-offs with shock mounts, and it was pretty hard to get to.  I ended up removing air cleaner and the air cleaner mounting brackets to access it.  Even so, getting to the bottom right bolt was quite a challenge.  It's up against the engine mount secured against the C-beam.  I finally got a box wrench on it coming in from a very narrow passage from the transmission (coach front) side.  The 70-pin connectors are 4mm (~5/32") allen head bolts.  There's a braided ground wire that attaches from the starter to the top left bolt and routes from the starter between the J1 and J2 connectors to the top left bolt.  A smaller braided wire also attaches to that bolt and is secured to the case of the ECM.

The one up-side to each challenge I encounter is that I know the coach better than I did before I had the problem.  That could end up really helping me one day if I need to make a trail fix somewhere. 

Thanks again for everyone's input!

[Eric Maclean]

Bill
The place you are sending the ECM out to will need some info from you is
1 ) the ECM serial number
2) rear end ratio
3) tire size
4) transmission make model
5) idle speed
6) engine max speed
7) cooling fan configuration
jake brake con if any
9)max road speed set if any
@0) max cruise speed if set

If the the rebuilder is  cat licenced they should be able to get programming from cat using your ECM serial number.
Usually it easier with a working ECM to retrieve the existing programing
At any rate I'm sure a reputable rebuilder will be able to get you set up with exceptable programing .

PS.. nice spot to work in down there isn't it even worse with grease and road grime.
        Make sure to keep those ECM connectors clean and inspect all the pins for bent or corrosion.
        Don't loose the bolts or stand offs.
Keep us informed as to your progress
Good luck
Eric