P2637: Torque management feedback signal A problem between engine and transmission computers
Torque management feedback signal A
Severity: Severity not verified — if the car runs badly, have it inspected
The sources describe the fault on heavy-duty vehicles but do not rate drivability or safety.
It gets more serious if:
- Inspect soon: Get it inspected soon if the transmission shifts harshly, goes into limp mode or the vehicle loses power.
P2637 in short
P2637 means the transmission computer is not getting the torque management feedback it expects from the engine computer. Likely causes include a communication or wiring fault, an engine or transmission computer software issue, or a faulty module. On Allison and Cummins equipment, an engine calibration update has fixed it.
Torque management lets the transmission ask the engine to briefly cut torque during shifts. The engine reports back with a feedback signal, called signal A here.
P2637 is set when that feedback is missing or wrong. Reference pages list wiring, communication and the transmission control module among the causes.
Cummins bulletins say the Allison fault P2637 can be caused by the engine control module calibration and is fixed by an update. This applies to heavy-duty equipment, so check your service information.
Most likely causes
Cause 1: Engine control module calibration (heavy-duty Cummins and Allison)
Supported by vehicle data- Why it ranks here
- Cummins bulletins say a calibration update stops P2637 on affected Allison-equipped engines, but the NHTSA summaries are short and status is not verified.
- What would change this
- Rises if your engine is a Cummins that a dealer finds out of date. Falls on other vehicles.
Cause 2: Wiring or data link fault between the engine and transmission computers
Common general cause- Why it ranks here
- Reference pages list wiring and communication faults for torque management signals.
- What would change this
- Rises if other communication codes are stored or the connectors are damaged. Falls if the network tests clean.
Cause 3: Transmission control module fault
Possible — needs testing- Why it ranks here
- A failed module is possible after wiring and software are cleared.
- What would change this
- Rises if everything else tests good. Falls otherwise.
What to test first
Start at step 1. Each result tells you what it means and where to go next.
Step 1: Read codes from both the engine and transmission modules and note any communication codes.
IfCommunication codes are present
It meansCheck the network wiring and connectors.
Points to: Wiring or data link fault between the engine and transmission computers
IfP2637 alone
It meansAsk about a calibration update.
Step 2: Ask a dealer whether the engine and transmission software are up to date for your VIN.
IfA calibration update is available
It meansUpdate before replacing parts.
Points to: Engine control module calibration (heavy-duty Cummins and Allison)
IfSoftware is current
It meansHave the module tested.
Symptoms
- Check engine or transmission warning light
- Harsh or odd shifting
- Loss of power or limp mode Gets more serious: stop and have it checked.
How to fix
Step 1: Ask a dealer whether the engine and transmission software for your VIN are current.
Parts and cost context
- Transmission control module (TCM):A last resort after wiring and software. Labour varies; get a quote.
Labor varies by vehicle and shop; get a quote before you approve a repair.
Compare used part prices on PartPriceGuideOn your vehicle
We don't have reviewed vehicle-specific evidence for P2637 yet. The causes and tests above apply across vehicles.
Related codes
No curated relationships for P2637 yet.
Sources and review
- P2637 trouble code explanation
- Cummins TSB210020-012920: Allison P2637 caused by engine control module calibration
- Cummins TSB170089-071720: Allison transmission control module sets P2637
- P2637 OBD-II trouble code
- Last reviewed
- Written by
- Saurabh K.
- Editorial review
- Pending
- Technician review
- Technician review pending
This page explains what a code usually means; it is not a substitute for a professional inspection. How we source and review · Report an error