Allison 1000 Transmission

[Thudman]

A while back on this forum, there was a discussion about PCM (Powertrain Control Module) and TCM (Transmission Control Module). A friend recently experienced an operator-induced problem: on a downhill run, he inadvertently shifted into Reverse (for a split second). Everything in the coach shut down: engine, transmission, et al. Fortunately he maintained control & stopped. But the rig was dead....no start. Spent six hours calling Good Sam, WH, coach mfr with no luck. Long story short, an old time truck mechanic fixed the problem in ten seconds, by resetting either the PCM or TCM, under the chassis just aft of the LF wheel.

My questions are: which is it PCM or TCM; and where/what switch/button is to be reset. This has occurred to two WH owners in this RV park.

Thudman

[Thudman]

A while back on this forum, there was a discussion about PCM (Powertrain Control Module) and TCM (Transmission Control Module). A friend recently experienced an operator-induced problem: on a downhill run, he inadvertently shifted into Reverse (for a split second). Everything in the coach shut down: engine, transmission, et al. Fortunately he maintained control & stopped. But the rig was dead....no start. Spent six hours calling Good Sam, WH, coach mfr with no luck. Long story short, an old time truck mechanic fixed the problem in ten seconds, by resetting either the PCM or TCM, under the chassis just aft of the LF wheel.

My questions are: which is it PCM or TCM; and where/what switch/button is to be reset. This has occurred to two WH owners in this RV park.

Thudman

[DriVer]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Thudman:
My questions are: which is it PCM or TCM; and where/what switch/button is to be reset. This has occurred to two WH owners in this RV park. </div></BLOCKQUOTE>Thudman, On our model of chassis we have both an ECM and a TCM and no PCM. The ECM is an Engine Control Module and the TCM is a Transmission Control Module. Both of these computers are seen on the upper centerline facing the engine. The TCM is always located on top and the ECM is located below. In later years with the introduction of the 6 speed Allison the TCM's case has been reduced in size and the heat sink has many vertical small vertical spines.

A PCM is a Powertrain Control Module and it is used on all P Series and other Workhorse Chassis which are not equipped with an Allison transmission. The PCM controls both the engine and GM transmission. These transmissions are typically the 4L80E and the 4L85E. The gas Engine can be a 7.4, 8.1 or the 6.0L. I also believe that the Front diesel P32s had a PCM as well as it was equipped with a GM transmission.

Regarding a reset switch, I am not aware of a reset switch location on vehicles equipped with either a ECM or PCM.

Thudman, I was recently pleased to visit the USAF Museum at Wright Pat and I saw a Thud in both fighter bomber and in Wild Weasel trim.

[al koffman]

Driver, could those modules be reset by disconnecting the chassis battery for 10-15 seconds?

[DriVer]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by al koffman:
Driver, could those modules be reset by disconnecting the chassis battery for 10-15 seconds? </div></BLOCKQUOTE>al, I'm not sure but if I were going to go for a cold start I would no doubt disconnect the battery for at least 5 minutes but I don't have any hard data to sustain that statement.

The ECM & PCM are EEPROM type computers and won't loose their programming. What would be reset would be what the computer has learned. The computer should start up with a clean slate and it'll have to re-learn your driving habits.

[al koffman]

I realize that the program would not change, thought that the cold startup might clear out any temp locations that store the data that is causing the hickup. Certainly worth a try.

[Ray,IN]

I can't speak for the GM computers, however the Dodge computers may be reset to factory programming by disconnecting both batteries for a minimum of (varies) 20 minutes to 1 hour.

[DriVer]

I have recently come to find out that you physically have to disconnect the cables off of the ECM in order to reset it. Source was WCC service center.

[DriVer]

I recently have sustained a lightning strike. At this time it is believed that my Allison TCM is fried.

The following anomalies are present:
<LI> The IP shift quadrant displays "D" only in any gear.
<LI> The transmission does not down shift via throttle changes and or elevated TPS (throttle position sensor) in cruise.
<LI> The transmission will clunk when automatically downshifting from 2nd to 1st.
<LI> I am told that when the Tech II was connected to the OBDII port - it could not see the TCM.

In order for me to get from Forest City to my present location I had to manually drive my motorhome by means of watching the Scan Gauge II "TPS" function. As soon as the TPS value exceeded 65 to 70, I switched OFF my OD lockout switch which then called for a downshift to 4th and accelerated the vehicle up a grade. If 4th gear was not sufficient and I found myself scrubbing any RPM or Speed by again observing my Scan Gauge II I manually down shifted to 3rd using my shifter.

The transmission did automatically shift upward from 1st to 5th somewhat normally from a stop however I believe that the shift schedule is compromised. I start off by manually selecting gears using my shifter I was able to come up to speed more rapidly by keeping the selected gear engaged longer and pulling more revs before up-shifting.

Manually shifting works well but it's attention and labor intensive as opposed to "automatic".

There is no "Range Inhibit", transmission lamp lit or any other message in the IP concerning an EC or Error Code (condition). The tranny is not even in limp mode after having sustained a lightning strike.

We are waiting to have a blank TCM programmed for our 2003 transmission on Monday and we should be on our way to South Carolina on Monday afternoon - IF all goes according to plan.

We are expecting that everything will go well. Looks like the Allison Transmission takes a really hard licking and keeps on ticking! Don't leave home without it!

[Thudman]

DriVer:

Curious as to why xmsn repairs were not made at Forest City?

Thudman

[DriVer]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Thudman:
Curious as to why xmsn repairs were not made at Forest City? </div></BLOCKQUOTE>A 2 hour diagnostic session was applied and they initially told me that the TCM is probably defective. They took it for a test drive with a Tech II attached and they said that it appeared to be shifting OK.

I had previously driven the MH to Customer Service and I felt that at the very least I can still move this thing however the symptoms that I wrote about were not in evidence at that time.

WGO had offered that they didn't have a replacement TCM in stock (since the TCMs are unique to the year of mfg) and it would have taken quite some time to have a unit flashed and shipped to Forest City. I made a command decision to depart the AO and proceed en-route to our current destination.

[cvrvr]

DriVer

I am curious. Did lightning actually strike your MH or was the surge induced thru shore power hook up?

Hope you get every thing back to normal.

Here in Southern California is one thing we don't have to worry about.

George

[DriVer]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by cvrvr:
I am curious. Did lightning actually strike your MH or was the surge induced thru shore power hook up? </div></BLOCKQUOTE>George, We did take a direct hit. Our FireStik CB antenna was struck and it exploded the copper windings off the antenna shaft. An observer noted that after the strike our antenna was observed smoldering!

The strike came in through the CB antenna and out through the electrical system to the pedestal.

[al koffman]

Driver, you sure got my curiosity up. If you disconnect the battery and still have to remove the cables from the ECM to reset it, where is the power coming from that makes it necessary to disconnect the cables to the ECM?