Heavy Duty Truck Scan Tool for Allison Transmissions

When an Allison-equipped work truck locks in one gear, shifts hard, or lights CHECK TRANS on the dash, the first question is what code the transmission controller stored. A basic engine code reader often cannot answer that on a medium- or heavy-duty truck. This handheld HD601 talks to heavy-duty controllers over SAE J1939 and J1708 and to cars and light trucks over standard OBD2, so the transmission controller is on the menu next to the engine, ABS and brake systems. It works on Allison and Eaton units in Class 4 through Class 8 trucks from Freightliner, International, Peterbilt, Paccar and Ford, among others.

What the scan tool does on an Allison

An electronically controlled Allison is run by its transmission control module. When the TCM sees a problem, Allison says it restricts shifting, turns on the warning light and records a diagnostic code. The light is labeled CHECK TRANS on vehicles not subject to OBD II rules, and it is the MIL on vehicles that are. On a commercial truck, the TCM shares the J1939 or J1708 data link with the engine and brake controllers. Plug this tool into the 6-pin or 9-pin Deutsch connector, key on, choose the transmission system, and it pulls stored and pending codes, freeze frame and live data. The 2.8 inch color screen shows the code definition from the built-in library, so you are not searching a code book at the fender. It runs on both 12V and 24V systems and comes with 6-pin, 9-pin and 16-pin OBD2 cables.

Problems it helps you sort out

• CHECK TRANS or MIL on with no obvious cause
• Truck locked in one range, or a range inhibit light on: the TCM holds the gear and drops converter lockup when it sees a fault
• Harsh shifts or flares, where the code tells you whether it is a solenoid circuit, a speed sensor or a ratio fault
• Lockup slip or shudder complaints, such as a TCC slip code like P0741 on an OBD2 vehicle
• Clearing stored codes after a repair, then confirming they stay gone on the road test

Before you buy: confirm it can reach your truck

Check the diagnostic connector first. A round 6-pin or 9-pin Deutsch plug under the dash means J1708 or J1939, and the tool includes both cables. A 16-pin OBD2 port means it will talk over the OBD2 protocols it supports, which include ISO 15765-4 (CAN), ISO 14230-4 and ISO 9141-2. The limit is J1850: this tool does not support J1850 PWM or J1850 VPW. CAN became the required OBD2 protocol for all US vehicles from the 2008 model year, so the gap mainly hits older domestic cars and light trucks. That matters for early GM pickups with the Allison 1000, so check that your truck communicates on CAN before you count on it for a Duramax. If you are working through a lockup complaint, start with our Allison 1000 torque converter shudder guide, and for a truck stuck in one gear, read the Allison limp mode causes guide.

Fitment and what it does not do

Coverage per the listing: Class 4 through Class 8 trucks with J1939 or J1708, plus OBD2 cars and light trucks on the protocols above, 12V or 24V. It reads and clears transmission, engine, ABS, brake system, ESP, EPS and fuel system codes. The listing does not claim Allison-specific service functions. Allison's own operator manual notes that some features, such as resetting the prognostics oil life and filter monitors and clearing the codes those features set, need the Allison DOC service software. Plan on a dealer or Allison DOC for those jobs. Browse the Allison parts collection for the repair parts that usually follow a scan.

Using it on a repair

• Read and write down every code before clearing anything. Several codes together often point to one cause, such as low voltage.
• If the code is a solenoid circuit fault, check the connector and harness before buying parts. If the solenoid itself has failed, the Allison 1000/2000 7-piece solenoid kit replaces the full set on Duramax trucks.
• Shift quality codes that return after solenoid work usually lead into the valve body. Our valve body testing guide covers the sticking valves behind codes like P0872.
• Check the fluid level and condition on any code that involves pressure or temperature before going further.
• Clear codes, road test through every range, then re-scan to confirm the repair held.

Will this read the Allison 1000 in my Duramax pickup?

On a pickup it works through the 16-pin OBD2 port, and only on the protocols it supports. It does not support J1850 VPW or PWM, so confirm your truck communicates on CAN (required on all US vehicles from the 2008 model year) before relying on it.

Which connector does my truck have?

Most medium- and heavy-duty trucks use a round 6-pin (J1708) or 9-pin (J1939) Deutsch connector under the dash. Light trucks and cars use the 16-pin OBD2 port. All three cables are in the box.

Can it clear transmission codes?

Yes, it reads and clears codes on Allison and Eaton units. Allison notes that some prognostics resets and the codes those features set need the Allison DOC service software, so a dealer tool may still be needed for those.

Does it work on 24-volt trucks?

Yes. It runs on both 12V and 24V systems, so the same tool covers a light-duty pickup and a Class 8 tractor.

Does it do a transmission relearn?

The listing covers reading and clearing codes, freeze frame and live data. It does not claim adaptive relearn or other Allison-specific service routines, so do not buy it for that job alone.

• Allison 1000 Limp Mode: Causes and How to Diagnose It
• Allison 1000 Torque Converter Shudder: Diagnosis and Fix
• Allison 1000 Valve Body Problems: Symptoms, How to Test, and Replacement
• Allison 1000 Fluid and Filter Service: Real Capacities, Intervals, and the TES 668 Change