Allison 1000 & 2000 Gen 5 Fault Code:P2670 Actuator Supply Voltage 2 (HSD2) – Low

CIRCUIT DESCRIPTION:
HSD2 supplies battery voltage to PCS2, SS1, SS2, SS3 via wire 171. HSD2 is continuously on during normal operation except during brief circuit tests. The TCM regulates control current to the solenoids by switching the appropriate low side driver on and off. DTC P2670 indicates the TCM has detected that all solenoids connected to the HSD2 are inactive with a supply voltage in the HSD2 circuit lower than a calibrated voltage. DTC 2670 indicates a short-to-ground has occurred in the high side wiring attached to HSD2 (wire 171).

ACTION TAKEN WHEN THE DTC SETS:
When DTC P2670 is active, the following conditions occur:
1. If failure occurs while in a forward range shift to 1st, 3rd, or 5th range is made.
2. While diagnostic response is active, if shift selector is moved to N (Neutral), transmission shifts to neutral; if the shift selector is moved to R (Revere), transmission shifts to reverse. If the shift selector is moved to D (Drive) range or R (Reverse) and transmission is compromised by overspeeding or direction change, transmission shifts to neutral.
3. Torque Converter Clutch (TCC) engagement is inhibited.
4. The DTC is stored in the TCM history.
5. The CHECK TRANS light illuminates.
6. The TCM forces Variable Modulated Main off.
7. The TCM freezes shift adapts (DNA).

CONDITIONS FOR CLEARING THE DTC:
Use the diagnostic tool to clear the DTC from the TCM history. The TCM automatically clears the DTC from the TCM history if the vehicle completes 40 warm-up cycles without the DTC recurring.

DIAGNOSTIC AIDS:
The following procedures are not documented in any OEM procedures or in any OEM Troubleshooting or Service information and should not be used as a method to diagnose any transmission DTCs, function, or shift quality concern:

1. Back-probing any connections used for transmission features or functions may damage and/or unlock terminals from the back-probed connector creating permanent or intermittent shorts and/or open circuits. If possible, use the J-39700 Breakout Box, the appropriate harness adapters, and appropriate magnetic overlays to troubleshoot the vehicle.

2. Load-testing any transmission-related circuits with any other electrical devices such as vehicle lamps or relays, especially with the TCM connected to the harness. Use J-39700 Breakout Box and appropriate harnesses with the diagnostic tool to monitor the circuit performance in question unless otherwise specified in the various Troubleshooting information.

3. Piercing a wire to check for voltages, shorts-to-grounds or other wires anywhere in the circuit but especially at the TCM. This creates a leak path for moisture and damages the wire and insulation.

4. The high side drivers (HSD1 and HSD2) reset opening the high side circuit whenever a short-to-ground is detected.

Inspect the wiring for poor electrical connections at the TCM and the transmission main connector. Look for the following conditions:
1. A bent terminal.
2. A backed-out terminal.
3. A damaged terminal.
4. Poor terminal tension.
5. A chafed wire.
6. A broken wire inside the insulation.

Inspect OEM wiring harness routing. Look for possible contact points where chafing could occur leading to an open circuit condition. Moving parts on the vehicle could be contacting the harness; this includes parking brake drum, suspension components, transmission shift linkage, etc.

When diagnosing for an intermittent open condition, massage the wiring harness while watching the test equipment for a change.

You may have to drive the vehicle in order to experience a fault. Use the data obtained from failure records to determine transmission range and/or certain vehicle operating variables such as temperature, run time, etc. This data can be useful in reproducing the failure mode when the DTC was set.