because all motor speed sensor shield wires
are spliced together.
NOTE: The vehicle OEM has responsibility
for all external wiring harness repair. Harness
repairs performed by Allison Transmission
distributors and dealers are not covered by
Allison Transmission warranty.
Were any shorts­to­ground or shorts to any
other wires found?
14

1.
2.

3.
4.
5.

Leave the ignition OFF.
Connect the J­50165, DPIM2 Adapter
Harness, to the red/blue DPIM 32­way
connector. Leave it connected to the
red/blue OEM 32­way connector and
leave the P1 and P2 encoder connectors
disconnected.
Turn ON the ignition.
Measure sensor supply voltage at the
P1 encoder connector on pin C.
Measure sensor supply voltage at the
P2 encoder connector on pin C.

DPIM1
10­13V
DPIM2
7.5­18V
(nominal ~12V)

NOTE: The vehicle OEM has responsibility
for all external wiring harness repair. Harness
repairs performed by Allison Transmission
distributors and dealers are not covered by
Allison Transmission warranty.
Were both voltages within the specified range?
15

1.
2.

Turn OFF the ignition.
Leave the P1 and P2 encoder connectors
disconnected.
3. Use J­39197, Jumper Wire Kit, to measure
resistance to ground on pin B of the
P1 encoder connector.
4. Use J­39197, Jumper Wire Kit, to measure
resistance to ground on pin B of the
P2 encoder connector.
Were the measured resistance values within
specification?

Less than 4
Ohms

Copyright © 2015 Allison Transmission, Inc. All Rights Reserved.

5­541

Allison H 40/50 EP

DTC 73–37 Inverter A Loss of Both Encoder Signals (cont’d)
Step
16

Action
1.
2.
3.
4.
5.

6.

7.

Leave the ignition OFF.
Leave the P1 and P2 encoder connectors
disconnected.
Use J­39197, Jumper Wire Kit, to jumper
pins A and C on the P1 encoder connector.
Use J­39197, Jumper Wire Kit, to jumper
pins A and C on the P2 encoder connector.
Disconnect the red/blue DPIM 32­way
connector from J­50165, DPIM2 Adapter
Harness, leaving J­50165 mated to the
red/blue OEM 32­way connector.
At J­50165­3, DPIM2 Overlay, measure
the resistance between pins 6 and 10 of
the red/blue OEM 32­way connector.
At J­50165­3, DPIM2 Overlay, measure the
resistance between pins 7 and 9 of the red/
blue OEM 32­way connector.

Value(s)

Yes

No

Less than 4
Ohms

Go to Step 17

Open or short in
vehicle harness.
Repair as
necessary and
go to Step 20

Less than 4
Ohms

Go to Step 18

Open or short in
vehicle harness.
Repair as
necessary and
go to Step 20

Go to Step 20

Replace the
speed sensor.
Go to Step 20

NOTE: The vehicle OEM has responsibility
for all external wiring harness repair. Harness
repairs performed by Allison Transmission
distributors and dealers are not covered by
Allison Transmission warranty.
Were the measured resistance values within
specification?
17

1.
2.
3.
4.
5.
6.

7.

8.

Leave the ignition OFF.
Leave the P1 and P2 encoder connectors
disconnected.
Remove the jumper wire from the P1 and
P2 encoder connectors.
Use J­39197, Jumper Wire Kit, to jumper
pins A and B on the P1 encoder connector.
Use J­39197, Jumper Wire Kit, to jumper
pins A and B on the P2 encoder connector.
Leave the J­50165, DPIM2 Adapter
Harness, mated to the red/blue OEM 32­way
connector ONLY.
At J­50165­3, DPIM2 Overlay, measure the
resistance between pins 10 and 22 of the
red/blue OEM 32­way connector.
At J­50165­3, DPIM2 Overlay, measure the
resistance between pins 7 and 25 of the
red/blue OEM 32­way connector.

NOTE: The vehicle OEM has responsibility
for all external wiring harness repair. Harness
repairs performed by Allison Transmission
distributors and dealers are not covered by
Allison Transmission warranty.

18

5­542

Were the measured resistance values within
specification?
Replace the P1 and P2 speed sensors.
Have the speed sensors been replaced?

Copyright © 2015 Allison Transmission, Inc. All Rights Reserved.

Section 5—DIAGNOSTIC CODES

DTC 73–37 Inverter A Loss of Both Encoder Signals (cont’d)
Step

Action

19

NOTE: In most cases, the Dual Power Inverter
Module (DPIM) is not at fault. Investigate
thoroughly before replacing the DPIM.

Value(s)

Yes

No

Go to Step 20

Replace DPIM.
Go to Step 20

Begin the
diagnosis again.
Go to Step 1

System OK

Replace DPIM. Contact Technical Assistance
Center (TAC) at 1­800­252­5283 for
DPIM replacement authorization. TAC will
require a snapshot.
Is the replacement of the DPIM complete?
20

To verify the repair:
1. Clear the DTC.
2. Operate the vehicle under normal driving
conditions.
Did the DTC return?

Copyright © 2015 Allison Transmission, Inc. All Rights Reserved.

5­543

Allison H 40/50 EP

DTC 73–38 Inverter A Secondary Encoder Signal Lost

Figure 5–46.
Overview:
This DTC is logged when the speed signal is lost or intermittent from the P1 motor speed sensor.
Action Taken When DTC Sets:
When DTC 73­38 is active, the following conditions will occur:
• MIL light illuminates
• Check System light illuminates
• Disable Inverter A
– Inverter A CAN enable will be removed. Vehicle can limp home on one motor only.
• Disable special mode
– HUSHTM mode will be disabled
Possible Causes:
• Open/break in 12V supply or signal harness
• Loss of sensor ground
• Bad sensor
• Internal DPIM fault
Tool Requirements:
• Universal Allison DOC®
• J­39700 Universal Breakout Box
5­544

Copyright © 2015 Allison Transmission, Inc. All Rights Reserved.

Section 5—DIAGNOSTIC CODES

DTC 73–38 Inverter A Secondary Encoder Signal Lost (cont’d)
• J­46711 TCM/VCM/DPIM Breakout Harness
• J­50165 DPIM2 Adapter Harness
• J­46708 Multimeter
• J­39197 Jumper Wire Kit
NOTE: DPIM2 has a blue Motor A Terminal Protection Assurance (TPA) key and J­46711,
TCM/VCM/DPIM Breakout Harness, has a red Motor A TPA key. When servicing a DPIM2, use
J­50165, Adapter Harness, with J­46711, TCM/VCM/DPIM Breakout Harness. This will convert the
J­46711’s red connector TPA key to a blue connector TPA key and allow it to connect to a DPIM2.

Step

Action

1

Are any 13­XX series DTCs set along with this
code?

2

1. Install Universal Allison DOC®.
2. Start the engine.
3. Record the DTC snapshot.
4. Monitor TCM ignition voltage.
Is the voltage within the specified values?

3

Value(s)

Yes

No

Troubleshoot
these codes first.

Go to Step 2

Go to Step 3

Resolve voltage
problem. Go to
Step 20

Is DTC 73­38 active?

Go to Step 5

Go to Step 4

4

1.
2.

Clear the DTC.
Attempt to duplicate the conditions in the
failure record (mode, temperature, etc.).
Does DTC 73­38 return?

Go to Step 5

System OK

5

Perform a visual inspection of P1 sensor OR
both P1 and P2.

Make repairs as
necessary and
go to Step 20

Go to Step 6

9–18V

NOTE: The vehicle OEM has responsibility
for all external wiring harness repair. Harness
repairs performed by Allison Transmission
distributors and dealers are not covered by
Allison Transmission warranty.
Is there any water intrusion, damaged wiring,
etc. that may cause a loss and/or corruption of
signal?
6

1.
2.

Turn OFF the ignition.
Install J­39700, Universal Breakout
Box, to the DPIM 24­way and the
OEM 24­way connectors using J­46711,
TCM/VCM/DPIM Breakout Harness.
3. Turn ON the ignition.
Is the harness connected and the ignition turned
back ON?

Go to Step 7

Copyright © 2015 Allison Transmission, Inc. All Rights Reserved.

5­545

Allison H 40/50 EP

DTC 73–38 Inverter A Secondary Encoder Signal Lost (cont’d)
Step
7

Action
At J­46711­1, DPIM Overlay, measure battery
supply voltage on pins 1, 2, 5, and 6 of the
DPIM 24­way connector.

Value(s)

Yes

No

10.5–16V

Go to Step 8

Open or short in
vehicle harness.
Repair as
necessary and
go to Step 20

9–16V

Go to Step 9

Open or short in
vehicle harness.
Repair as
necessary and
go to Step 20

9–16V

Go to Step 10

Open or short in
vehicle harness.
Repair as
necessary and
go to Step 20

Less than 4
Ohms

Go to Step 11

Open or short in
vehicle harness.
Repair as
necessary and
go to Step 20

NOTE: The vehicle OEM has responsibility
for all external wiring harness repair. Harness
repairs performed by Allison Transmission
distributors and dealers are not covered by
Allison Transmission warranty.
Is the voltage within the specified range?
8

At J­46711­1, DPIM Overlay, measure wakeup
signal voltage on pins 3 and 4 of the 24­way
connector.
NOTE: The vehicle OEM has responsibility
for all external wiring harness repair. Harness
repairs performed by Allison Transmission
distributors and dealers are not covered by
Allison Transmission warranty.
Is the voltage within the specified range?

9

At J­46711­1, DPIM Overlay, measure torque
enable voltage on pins 16 (Inverter B Torque
Enable) and 17 (Inverter A Torque Enable) of
the 24­way connector.
NOTE: The vehicle OEM has responsibility
for all external wiring harness repair. Harness
repairs performed by Allison Transmission
distributors and dealers are not covered by
Allison Transmission warranty.
Is the voltage within the specified range?

10

1.
2.

3.

Turn OFF the ignition.
Disconnect the J­46711, TCM/VCM/
DPIM Breakout Harness, from the
DPIM 24­way connector. Leave the
OEM 24­way connector mated to the
J­46711.
At J­46711­1, DPIM Overlay, measure
resistance to ground on 12V battery return
pins 18, 19, 20, and 21 of the DPIM 24­way
connector.

NOTE: The vehicle OEM has responsibility
for all external wiring harness repair. Harness
repairs performed by Allison Transmission
distributors and dealers are not covered by
Allison Transmission warranty.
Was the resistance within specification?

5­546

Copyright © 2015 Allison Transmission, Inc. All Rights Reserved.

Section 5—DIAGNOSTIC CODES

DTC 73–38 Inverter A Secondary Encoder Signal Lost (cont’d)
Step
11

12

Action

Value(s)

Yes

No

Leave the ignition OFF.
Disconnect the DPIM 24­way and
OEM 24­way connectors from the J­46711,
TCM/VCM/DPIM Breakout Harness.
3. Connect the OEM 24­way connector to the
DPIM 24­way connector.
4. Disconnect the red/blue OEM 32­way
connector from the DPIM.
5. Connect the red/blue DPIM 32­way
connector of the J­46711, TCM/
VCM/DPIM Breakout Harness, using
J­50165, DPIM2 Adapter Harness, to
the DPIM connector ONLY. Leave the
J­46711 disconnected from the red/blue
OEM 32­way connector.
6. Turn ON the ignition.
7. At J­50165­3, DPIM2 Overlay, measure the
speed sensor supply Open Circuit Voltage
(OCV) at the red/blue 32­way connector
by measuring the voltage between pin
6 and pin 22 of the red/blue 32­way DPIM
connector.
Is the voltage within the specified range?

DPIM1
10­13V

Go to Step 12

Go to Step 19

Short in vehicle
harness. Repair
as necessary and
go to Step 20

Go to Step 13

1.
2.

1.
2.

3.

4.
5.

Turn OFF the ignition.
Disconnect the J­50165, DPIM2 Adapter
Harness, from the red/blue DPIM 32­way
connector.
Connect the J­50165, DPIM2 Adapter
Harness, to the red/blue OEM 32­way
connector ONLY.
Turn ON the ignition.
At J­50165­3, DPIM2 Overlay, measure for
voltage on pins 6, 10, 8, and 22.

DPIM2
7.5­18V
(nominal ~12V)

NOTE: The vehicle OEM has responsibility
for all external wiring harness repair. Harness
repairs performed by Allison Transmission
distributors and dealers are not covered by
Allison Transmission warranty.
Was voltage measured on any of the pins?

Copyright © 2015 Allison Transmission, Inc. All Rights Reserved.