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SpeedlabDan

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Ok guys it seems after this engine swap my Allison is in limp mode. Locked in 3rd with full line psi.
As far as I can tell with my simple code reader the tcm is requesting illumination from the ecm.
I'm still using the factory Allison tcm and harness removed by howell EFI and mated with the new 8.1L engine harness. The shift selector switch is used using the smaller plug but the larger upper is now just a pigtail. After a call to howell they state its outgoing only to the factory body control module and I no longer need it. I'm suspicious but I had hoped they are right. That's not to say this is the problem but a don't know where to start as far as diagnosis. What can cause limp mode? I hear signals can get scrambled from water in the connection, it's dry. Vss also seems to be working fine. Where do I go from here? Anybody swap an Allison have these issues? Thanks in advance
 

sweetk30

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were there any wires to tie in with the brake pedal switch on your swap ? if not this might be a problem . trans needs to know when brakes are on/off to do its thing .
 

SpeedlabDan

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were there any wires to tie in with the brake pedal switch on your swap ? if not this might be a problem . trans needs to know when brakes are on/off to do its thing .
Good point but I do y recall anytbi g unless it was hardwired from factory and now removed from the body harness
 

sweetk30

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years ago i got a harnness standalone kit i cant recall who was name brand back then . did a 4l80-e swap in a 2wd . didnt shift right . headed down to the local trans guy . he said were is my obd 1 or 2 plug so i can read problems ? and were is the brake light tie in wire ?

i called the company and they said oh sorry we forgot them . sent them out and i pluged them in and no problems after brake light switch tie in .
 

SpeedlabDan

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years ago i got a harnness standalone kit i cant recall who was name brand back then . did a 4l80-e swap in a 2wd . didnt shift right . headed down to the local trans guy . he said were is my obd 1 or 2 plug so i can read problems ? and were is the brake light tie in wire ?

i called the company and they said oh sorry we forgot them . sent them out and i pluged them in and no problems after brake light switch tie in .
I hope it's that simple. After a few calls to some Allison swap guys tomorrow I'll call howell again hopefully with more info. I already know they're gonna tell me they wired it the way it came out. Unfortunately it's up to me to know if it needs a brake wire or anything else that's missing. Too bad it's my first Allison swap so I'm at a loss
 

ZooMad75

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Larry's got NV4500's in both of his swaps. Hell, he's got the ZF 6-speed in his 8.1 Silverado. Without knowing what the TCM is seeing from the range switch you are going to be in the dark. As long as it can't tell the gear selection it's going to default.
 

SpeedlabDan

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Here are some useful wiring schematics I found for the "c1/c2" selector switch plugs. At the very least it shows that the outgoing signals from the larger plug shouldn't be the reason for issues in limp mode. I won't be able to get these codes scanned for a couple days.

images.png

images(2).png

IMG_20181118_205345.jpg

IMG_20181118_205415.jpg
 

Larry

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he has worked on them for years at his job thats how he knows 8.1 engines a lot . he might know or know someone who does . maybe even @Greg Ducato would know possibly .
Sorry, not much help from me. As Rob mentioned, all my swaps have been with manual transmissions but as far as Allison issues seen on Workhorse and International trucks going into default have been the usual power and ground issues, connection problems at the big connector at the transmission itself, wiring issues elsewhere or a dead or blanked out TCM. Being a swapped deal it could be so many things. Sorry, not much help from my angle.
 

SpeedlabDan

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Sorry, not much help from me. As Rob mentioned, all my swaps have been with manual transmissions but as far as Allison issues seen on Workhorse and International trucks going into default have been the usual power and ground issues, connection problems at the big connector at the transmission itself, wiring issues elsewhere or a dead or blanked out TCM. Being a swapped deal it could be so many things. Sorry, not much help from my angle.
Thanks @Larry, at this point I'm hoping it's the nsbu switch. As far as the harness, Howell assured me it's wired with the engine harness same as stock. As far as the large connector goes, there's one ground and one wire that he's to pcm that I should no longer need as all the body control stuff as been deleted. The vss is working perfectly as my speedometer is right on and the signal is coming from the Can low speed connector. A buddy is coming by with his programmer later today so fingers crossed its only something simple which the tcm should tell me. I'll update when I find out.
 

Kay86K5

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Sorry, not much help from me. As Rob mentioned, all my swaps have been with manual transmissions but as far as Allison issues seen on Workhorse and International trucks going into default have been the usual power and ground issues, connection problems at the big connector at the transmission itself, wiring issues elsewhere or a dead or blanked out TCM. Being a swapped deal it could be so many things. Sorry, not much help from my angle.

Thanks @Larry, at this point I'm hoping it's the nsbu switch. As far as the harness, Howell assured me it's wired with the engine harness same as stock. As far as the large connector goes, there's one ground and one wire that he's to pcm that I should no longer need as all the body control stuff as been deleted. The vss is working perfectly as my speedometer is right on and the signal is coming from the Can low speed connector. A buddy is coming by with his programmer later today so fingers crossed its only something simple which the tcm should tell me. I'll update when I find out.

I'm not help either as my 8.1 swap I did with an NV4500 as well. But I must say, some of these issues is a pretty big reason why I went manual instead of Allison on my swap. I had heard others have a hard time working through issues with the electronics on an Alisson swap, and then after reading a couple of @Larry's swaps and how simple they were, I decided a non-electronic manual transmission was looking pretty good.

Hopefully you get it figured out soon @SpeedlabDan
 

SpeedlabDan

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So here are the codes. Request illumination and high voltage shift selector are the only two to come back after clearing. I ordered a nsbu switch so well see if this fixes limpy.

IMG_20181121_182611.jpg

IMG_20181121_181709.jpg

IMG_20181121_181641.jpg
 

ZooMad75

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Here is the GM diagnostic for the P0708 code. You will need the scan too to see some of this data for the switch positions as in Step 3 and 4.


P0708
DTC P0708 (Two Connector NSBU)
Circuit Description
The installation of a transmission mounted neutral start/backup switch is required. This switch, commonly called a park/neutral position switch (PNP), mounts directly onto the transmission housing from the outside and detects the angular position of the shift selector shaft. This position is communicated to the transmission control module (TCM) so that certain vehicle control functions can be coordinated with the position of the shift controls. The PNP switch has redundant circuitry to alert the TCM in the event of a single wire or switch failure.

The neutral signal output of the PNP switch is typically used as confirmation that the transmission is in NEUTRAL before the engine starter is engaged. The PNP switch is interfaced to the starter circuit with weatherproof electrical connectors. The reverse signal provision may be used to activate vehicle back-up lights and/or reverse warning devices.

DTC P0708 is a type A DTC.

Conditions For Running The DTC
  • The components are powered and ignition voltage is greater than 9.0 volts and less than 18 volts.
  • Engine speed is greater than 200 RPM and less than 7,500 RPM for 5 seconds.
Conditions For Setting The DTC
DTC P0708 sets when the TCM detects an invalid condition and parity error occurring over consecutive ignition cycles.

Action Taken When The DTC Sets
While diagnostic response is active, one of the following conditions can occur :

  • The TCM illuminates the malfunction indicator lamp (MIL).
  • The transmission fails to hydraulic default.
  • DTC P0708 will be stored in TCM history.
  • The TCM freezes shift adapts.
  • The TCM inhibits torque converter clutch (TCC) engagement.
Conditions For Clearing The DTC
A scan tool must be used to clear the code from TCM history.

This DTC does not automatically clear from TCM history after 40 ignition cycles.

Diagnostic Aids
  • Inspect the wiring for poor electrical connections at the TCM and powertrain control module (PCM). Inspect for the following conditions:
    • A bent terminal
    • A backed-out terminal
    • A damaged terminal
    • Poor terminal tension
    • A chafed wire
    • A broken wire inside the insulation
  • When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change.
  • You may have to drive the vehicle in order to experience a condition.
  • If P0875, previously P1713, is shown in failure records as being set first on the failure list followed by P0872, previously P1711, combined with P0708, this generally indicates a PNP internal switch failure. Often, when the DTCs are cleared, they do not return. This may be due to moisture that was present at the time the DTC was set, causing a short internally.
  • Inspect the PNP switch linkage carefully for proper adjustment and for signs of damage.
Test Description
The numbers below refer to step numbers on the diagnostic table.

  1. 3
    This step tests TCM input response.

  2. 4
    This step tests the wiring harness for opens or shorts.

  3. 6
    This step tests the wiring harness for a short to voltage.
DTC P0708 (Two Connector NSBU)

Step Action Value Yes No
Schematic Reference: Automatic Transmission Controls Schematics
STEP 1 Did you perform the Diagnostic System Check - Automatic Transmission? - YES Go to Step 2 NO Go to Diagnostic System Check - Automatic Transmission
STEP 2 Inspect for proper adjustment of the park/neutral switch. Refer to Park/Neutral Position Switch Adjustment , and Shift Cable Adjustment.
Is the park/neutral position switch and shift linkage properly adjusted? - YES Go to Step 3 -
STEP 3
  1. Install the scan tool.
  2. Turn ON the ignition, with the engine OFF.
    IMPORTANT: Before clearing the DTC, use the scan tool in order to record the Freeze Frame and Failure Records for reference. The Clear Info function will erase the data.
  3. Record the DTC Freeze Frame and Failure Records.
  4. Clear the DTC.
  5. With the scan tool, observe the transmission range (TR) Sw. display while selecting each transmission range, P, R, N, D4, D3, D2, and D1.
Does each selected transmission range match the scan tool TR Sw. display? - YES Go to Diagnostic Aids NO Go to Step 4
STEP 4
  1. Turn the ignition OFF.
  2. Disconnect the 4-way connector at the PNP switch.
  3. Turn the ignition ON.
  4. In sequence, connect terminals 4A, 4B, 4C, and 4D in the 4-way PNP connector to terminal 7D in the 7-way PNP connector.
  5. Using the scan tool, monitor transmission range switch status.
Does each selected transmission range match the scan tool TR Sw. display? PARK = A and C
REVERSE = A and D
NEUTRAL = C and D
DRIVE 4= B and D
DRIVE 3 = A, B, C, D
DRIVE 2 = A and B
DRIVE 1 = B and C YES Go to Step 8 NO Go to Step 5
STEP 5
  1. Measure the voltage from terminal A of the TR switch 4-way connector to ground.
  2. Measure the voltage from terminal B of the TR switch 4-way connector to ground.
  3. Measure the voltage from terminal C of the TR switch 4-way connector to ground.
  4. Measure the voltage from terminal D of the TR switch 4-way connector to ground.

Does the voltage measure within the specified value at all four terminals? VALUE B+ YES Go to Step 6 NO Go to Step 7
STEP 6
  1. Turn the ignition OFF.
  2. Disconnect TCM connector C2 (RED).
  3. Using the DMM and the J 35616 , in sequence, test the signal circuits 5, 6, 7, and 8 of the TCM connector C2 (RED) and A, B, C, and D of the TR switch 4-way connector for a shorted together condition.
Refer to Circuit Testing , and Wiring Repairs in Wiring Systems.Did you find and correct the condition? - YES Go to Step 10 NO Go to Step 9
STEP 7 Test the signal circuits of the TR switch that did not indicate proper voltage for an open or short to ground. Refer to Circuit Testing , and Wiring Repairs in Wiring Systems.
Did you find and correct the condition? - YES Go to Step 10 NO Go to Step 9
STEP 8
IMPORTANT: A scan tool must be used in order to clear the code from TCM history.
Replace the PNP switch. Refer to Park/Neutral Position Switch Replacement .Did you complete the replacement? - YES Go to Step 10 -
STEP 9
IMPORTANT: In most cases, the TCM is not at fault. Investigate thoroughly before replacing the TCM.
Replace the TCM. Refer to Transmission Control Module Replacement .Did you complete the replacement? - YES Go to Step 10 -
STEP 10 Perform the following procedure in order to verify the repair:
  1. Clear the DTC.
  2. Using the scan tool, monitor the TR Sw. display while selecting each transmission range, P, R, N, D4, D3, D2, and D1.
  3. Select Specific DTC.
  4. Enter DTC P0708.

Has the test run and passed? - System OK Go to Step 1

Using the DMM and the J 35616 GM terminal test kit measure the following:
 

SpeedlabDan

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Here is the GM diagnostic for the P0708 code. You will need the scan too to see some of this data for the switch positions as in Step 3 and 4.


P0708
DTC P0708 (Two Connector NSBU)
Circuit Description
The installation of a transmission mounted neutral start/backup switch is required. This switch, commonly called a park/neutral position switch (PNP), mounts directly onto the transmission housing from the outside and detects the angular position of the shift selector shaft. This position is communicated to the transmission control module (TCM) so that certain vehicle control functions can be coordinated with the position of the shift controls. The PNP switch has redundant circuitry to alert the TCM in the event of a single wire or switch failure.

The neutral signal output of the PNP switch is typically used as confirmation that the transmission is in NEUTRAL before the engine starter is engaged. The PNP switch is interfaced to the starter circuit with weatherproof electrical connectors. The reverse signal provision may be used to activate vehicle back-up lights and/or reverse warning devices.

DTC P0708 is a type A DTC.

Conditions For Running The DTC
  • The components are powered and ignition voltage is greater than 9.0 volts and less than 18 volts.
  • Engine speed is greater than 200 RPM and less than 7,500 RPM for 5 seconds.
Conditions For Setting The DTC
DTC P0708 sets when the TCM detects an invalid condition and parity error occurring over consecutive ignition cycles.

Action Taken When The DTC Sets
While diagnostic response is active, one of the following conditions can occur :

  • The TCM illuminates the malfunction indicator lamp (MIL).
  • The transmission fails to hydraulic default.
  • DTC P0708 will be stored in TCM history.
  • The TCM freezes shift adapts.
  • The TCM inhibits torque converter clutch (TCC) engagement.
Conditions For Clearing The DTC
A scan tool must be used to clear the code from TCM history.

This DTC does not automatically clear from TCM history after 40 ignition cycles.

Diagnostic Aids
  • Inspect the wiring for poor electrical connections at the TCM and powertrain control module (PCM). Inspect for the following conditions:
    • A bent terminal
    • A backed-out terminal
    • A damaged terminal
    • Poor terminal tension
    • A chafed wire
    • A broken wire inside the insulation
  • When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change.
  • You may have to drive the vehicle in order to experience a condition.
  • If P0875, previously P1713, is shown in failure records as being set first on the failure list followed by P0872, previously P1711, combined with P0708, this generally indicates a PNP internal switch failure. Often, when the DTCs are cleared, they do not return. This may be due to moisture that was present at the time the DTC was set, causing a short internally.
  • Inspect the PNP switch linkage carefully for proper adjustment and for signs of damage.
Test Description
The numbers below refer to step numbers on the diagnostic table.

  1. 3
    This step tests TCM input response.

  2. 4
    This step tests the wiring harness for opens or shorts.

  3. 6
    This step tests the wiring harness for a short to voltage.
DTC P0708 (Two Connector NSBU)

Step Action Value Yes No
Schematic Reference: Automatic Transmission Controls Schematics
STEP 1 Did you perform the Diagnostic System Check - Automatic Transmission? - YES Go to Step 2 NO Go to Diagnostic System Check - Automatic Transmission
STEP 2 Inspect for proper adjustment of the park/neutral switch. Refer to Park/Neutral Position Switch Adjustment , and Shift Cable Adjustment.
Is the park/neutral position switch and shift linkage properly adjusted? - YES Go to Step 3 -
STEP 3
  1. Install the scan tool.
  2. Turn ON the ignition, with the engine OFF.
    IMPORTANT: Before clearing the DTC, use the scan tool in order to record the Freeze Frame and Failure Records for reference. The Clear Info function will erase the data.
  3. Record the DTC Freeze Frame and Failure Records.
  4. Clear the DTC.
  5. With the scan tool, observe the transmission range (TR) Sw. display while selecting each transmission range, P, R, N, D4, D3, D2, and D1.
Does each selected transmission range match the scan tool TR Sw. display? - YES Go to Diagnostic Aids NO Go to Step 4
STEP 4
  1. Turn the ignition OFF.
  2. Disconnect the 4-way connector at the PNP switch.
  3. Turn the ignition ON.
  4. In sequence, connect terminals 4A, 4B, 4C, and 4D in the 4-way PNP connector to terminal 7D in the 7-way PNP connector.
  5. Using the scan tool, monitor transmission range switch status.
Does each selected transmission range match the scan tool TR Sw. display? PARK = A and C
REVERSE = A and D
NEUTRAL = C and D
DRIVE 4= B and D
DRIVE 3 = A, B, C, D
DRIVE 2 = A and B
DRIVE 1 = B and C YES Go to Step 8 NO Go to Step 5
STEP 5
  1. Measure the voltage from terminal A of the TR switch 4-way connector to ground.
  2. Measure the voltage from terminal B of the TR switch 4-way connector to ground.
  3. Measure the voltage from terminal C of the TR switch 4-way connector to ground.
  4. Measure the voltage from terminal D of the TR switch 4-way connector to ground.

Does the voltage measure within the specified value at all four terminals? VALUE B+ YES Go to Step 6 NO Go to Step 7
STEP 6
  1. Turn the ignition OFF.
  2. Disconnect TCM connector C2 (RED).
  3. Using the DMM and the J 35616 , in sequence, test the signal circuits 5, 6, 7, and 8 of the TCM connector C2 (RED) and A, B, C, and D of the TR switch 4-way connector for a shorted together condition.
Refer to Circuit Testing , and Wiring Repairs in Wiring Systems.Did you find and correct the condition? - YES Go to Step 10 NO Go to Step 9
STEP 7 Test the signal circuits of the TR switch that did not indicate proper voltage for an open or short to ground. Refer to Circuit Testing , and Wiring Repairs in Wiring Systems.
Did you find and correct the condition? - YES Go to Step 10 NO Go to Step 9
STEP 8
IMPORTANT: A scan tool must be used in order to clear the code from TCM history.
Replace the PNP switch. Refer to Park/Neutral Position Switch Replacement .Did you complete the replacement? - YES Go to Step 10 -
STEP 9
IMPORTANT: In most cases, the TCM is not at fault. Investigate thoroughly before replacing the TCM.
Replace the TCM. Refer to Transmission Control Module Replacement .Did you complete the replacement? - YES Go to Step 10 -
STEP 10 Perform the following procedure in order to verify the repair:
  1. Clear the DTC.
  2. Using the scan tool, monitor the TR Sw. display while selecting each transmission range, P, R, N, D4, D3, D2, and D1.
  3. Select Specific DTC.
  4. Enter DTC P0708.

Has the test run and passed? - System OK Go to Step 1

Using the DMM and the J 35616 GM terminal test kit measure the following:
Good to know! Hopefully I'm within 40 ignition cycles so I donr have to have it cleared again if the switch solves the issue.
 

DSRE388

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Ok guys it seems after this engine swap my Allison is in limp mode. Locked in 3rd with full line psi.
As far as I can tell with my simple code reader the tcm is requesting illumination from the ecm.
I'm still using the factory Allison tcm and harness removed by howell EFI and mated with the new 8.1L engine harness. The shift selector switch is used using the smaller plug but the larger upper is now just a pigtail. After a call to howell they state its outgoing only to the factory body control module and I no longer need it. I'm suspicious but I had hoped they are right. That's not to say this is the problem but a don't know where to start as far as diagnosis. What can cause limp mode? I hear signals can get scrambled from water in the connection, it's dry. Vss also seems to be working fine. Where do I go from here? Anybody swap an Allison have these issues? Thanks in advance
Slippage in any gear, broken parts wrong wiring
 

SpeedlabDan

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Slippage in any gear, broken parts wrong wiring
No its not slipping and nothing seems broken. After the dtc was read from the tcm it appears to be the nsbu switch. After I receive the switch I'll clear codes and post back the results
 
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