P2638: Engine and transmission computers disagree on the torque signal
Torque management feedback signal A range/performance
Severity: Severity not verified — if the car runs badly, have it inspected
Our sources describe the symptoms (shifting trouble, stalling, a blinking gear indicator) but do not rate how safe it is to drive.
It gets more serious if:
- Inspect soon: Inspect soon if the transmission shifts hard or stays in one gear, the gear indicator blinks, or the engine stalls.
P2638 in short
P2638 means the torque signal exchanged between the engine and transmission computers is out of range or does not match. Causes include wiring or CAN faults, a failing control module, and on some Hondas a missed idle learn. Expect shifting trouble. Have it diagnosed soon, as severity is not verified.
The engine computer and transmission computer share a torque signal so shifts can be softened. When that signal is out of range or does not match, the code sets.
PartsAvatar lists a failed driver inside a control module, loose connections, shorted or corroded network wiring and a bad ground. Its symptom list includes shifting trouble, stalling and rough idle.
Honda's service news says that on a low-mileage 2016 Pilot with the MIL on and the gear position indicator blinking, P2638 is likely because the idle learn procedure was not done properly before delivery.
Most likely causes
Cause 1: Idle learn not completed (some Hondas)
Supported by vehicle data- Why it ranks here
- Honda's service news ties P2638 on a low-mileage 2016 Pilot with a blinking gear indicator to a missed idle learn.
- What would change this
- Rises if the code is on a low-mileage Pilot or followed a battery change. Falls if a proper idle learn is done and it returns.
Cause 2: Loose, corroded or shorted network wiring or a bad ground
Common general cause- Why it ranks here
- PartsAvatar lists loose connections, shorted or corroded network wiring and broken grounds.
- What would change this
- Rises if other communication codes are stored or the fault comes and goes. Falls if wiring and grounds test good.
Cause 3: Faulty engine or transmission control module
Possible — needs testing- Why it ranks here
- PartsAvatar lists a faulty driver in a control module as a cause, but it ranks below wiring and software until circuits test good.
- What would change this
- Rises only after wiring, grounds and software are ruled out.
What to test first
Start at step 1. Each result tells you what it means and where to go next.
Step 1: Read all codes from the engine and transmission modules, noting any network codes, and ask whether the idle learn was recently lost.
IfA Honda with the gear indicator blinking and no network codes
It meansAsk the dealer to run the idle learn procedure.
IfNetwork communication codes are stored too
It meansDiagnose the network wiring and grounds first.
Step 2: Inspect the engine and transmission connectors, grounds and network wiring for corrosion or looseness.
Warning:Disconnect the battery before unplugging modules, and avoid probing airbag circuits.
IfCorrosion, loose connectors or a bad ground
It meansRepair them and retest.
Points to: Loose, corroded or shorted network wiring or a bad ground
IfAll look good
It meansHave a shop test the modules.
Symptoms
- Shifting problems or a transmission stuck in one gear Gets more serious: stop and have it checked.
- Gear position indicator blinking
- Engine stalling or rough idle
- Check engine light
Compare with: Check engine light with loss of power
How to fix
Step 1: Ask a dealer whether the idle learn or a software update applies to your vehicle.
Parts and cost context
- Transmission control module (TCM):Module replacement is last. Test wiring and grounds first. Ask for a quote.
Labor varies by vehicle and shop; get a quote before you approve a repair.
Compare used part prices on PartPriceGuideOn your vehicle
HondaYour car
2016 · Pilot
Supported by vehicle dataHonda service news A15110F links P2638 and a blinking gear indicator on low-mileage 2016 Pilots to a missed idle learn. Whether it is still current is not verified.
A15110FStatus unverified
A/T DTC P2638 and idle learn
2016pilot · NHTSA 10100176
Service news: on a low-mileage Pilot with the MIL on and a blinking gear position indicator, the idle learn may not have been done properly before delivery. The NHTSA summary is short.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.
DodgeYour car
2003 · Ram
Supported by vehicle dataDodge bulletin 1802703 covers this code: no throttle response and low power when towing, P2638 and P0700. Whether it is still current is not verified.
1802703Status unverified
No throttle response and low power when towing, P2638 and P0700
2003ram · NHTSA 10003418
No throttle response and lack of power while towing with P2638 and P0700 stored on the 2003 Ram pickup.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.
Related codes
P2638 questions
Can a battery change cause P2638?
On some Hondas a lost idle learn is tied to this code. Ask a dealer to run the idle learn procedure.
Sources and review
- OBD Code P2638 - Torque Management Feedback Signal A Range/Performance
- Honda service news A15110F, A/T DTC P2638 and idle learn
- Dodge 1802703, No throttle response and low power when towing, P2638 and P0700
- 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