P1C64: On Ram 1500 eTorque trucks, the hybrid system saw the engine turn slower than its target when stop-start tried to restart it

Hybrid performance: engine speed below target during autostart

Severity: Inspect soon

FCA's bulletins describe an autostart that fails and leaves the transmission in limp mode, and owners report stalling in traffic, so book a dealer visit soon rather than ignoring it.

It gets more serious if:

Stop: Stop driving and call for help if the truck stalls, will not restart, or the battery light comes on; FCA describes a stall and loss of 12 V charging with the motor generator unit fault, and owners report stalling in traffic.

Source: how we rate severity

P1C64 in short

On the Ram 1500 eTorque, P1C64 means the engine did not reach its target speed when stop-start tried to restart it. Ram has issued hybrid controller software updates and a motor generator unit bulletin for it. Stalling is possible, so have a dealer check it soon, and stop driving if it stalls or will not restart.

The Ram 1500 eTorque is a mild-hybrid. A motor generator unit (MGU) helps spin the engine, and a hybrid control processor (HCP) manages automatic stop-start. When the engine is restarted after a stop, the HCP expects engine speed to climb to a target.

P1C64 sets when engine speed stays below that target during the automatic restart. Ram's bulletins pair it with a failed autostart, the transmission engaging park and a limp mode, and a different bulletin describes a stall, no restart and a lost 12-volt charge with the code.

Owners report the truck stalling in traffic or while towing, a lit check engine light, and stop-start and remote start being disabled. Dealers often cannot reproduce it, so keep the scan report and ask whether the bulletins below apply to your VIN.

Pick your make

P1C64 is a manufacturer-specific code: its meaning depends on who built the car.

Other makes: meaning not verified. Check with a scan tool that reads manufacturer definitions.

P1C64 on Ram

Most likely causes

Cause 1: Hybrid control processor software
Supported by vehicle data
Why it ranks here
Two Ram bulletins name P1C64 with U0402 and an autostart that fails, and the remedy is a software update. Bulletin status is unverified.
What would change this
Likelier on a 2022 Ram 1500 that also stored U0402 or has a failed autostart with the transmission in park or limp mode.
Cause 2: Motor generator unit or its connector
Supported by vehicle data
Why it ranks here
A Ram bulletin for 2020-2021 trucks lists P1C64 with MGU-related codes and a stall with no restart, and replaces the MGU. A later bulletin warns against replacing it for P1C64 or noise without a scan report. An owner reports the eTorque system was replaced and the stalling came back.
What would change this
Likelier on a 2020-2021 truck with MGU or resolver codes (P0A3F, P1B03, P0A92) or an underhood whine; less likely if only U0402 is stored.
How to test the hybrid drive motor

What to test first

Start at step 1. Each result tells you what it means and where to go next.

Step 1: Read stored, pending and permanent codes and save a scan report with freeze-frame data
Low riskTool: OBD-II scan tool that reads hybrid modules
- IfU0402 stored with P1C64
  It meansMatches the HCP software bulletins; ask a dealer to check your VIN.
  Points to: Hybrid control processor software
- IfP0A3F, P1B03, P0A92 or P0607 stored with P1C64 on a 2020-2021 truck
  It meansMatches the MGU connector bulletin; the dealer should inspect before replacing parts.
  Points to: Motor generator unit or its connector
- IfStalling, no restart or a battery light
  It meansStop driving and have it towed to a dealer.
  Go to step 2
Step 2: Ask a Ram dealer to check your VIN for open bulletins and software updates and to inspect the MGU connector before any part is replaced
Best left to a shopTool: Dealer scan tool (wiTECH)
Warning:The MGU and its harness belong to the hybrid system; leave connector inspection and unit replacement to a dealer, because unplugging them can set more codes and the circuits may still be energised.
- IfA software update is available
  It meansThe update is the bulletin remedy.
  Points to: Hybrid control processor software
- IfConnector or MGU fault found
  It meansRepair or replace per the bulletin.
  Points to: Motor generator unit or its connector

Symptoms

Check engine light
Stop-start and remote start disabled
Stalling at a stop or in traffic Gets more serious: stop and have it checked.
Engine will not restart Gets more serious: stop and have it checked.
Battery light Gets more serious: stop and have it checked.
Transmission goes to park or limp mode on restart

Compare with: Check engine light with loss of power

How to fix

Parts and cost context

Hybrid drive motor:One bulletin replaces the MGU and another asks dealers to document with a scan report first, so don't buy one on the code alone. Labour varies; get a quote.

Labor varies by vehicle and shop; get a quote before you approve a repair.

Compare used part prices on PartPriceGuide

On your vehicle

Ram

2019–2022 · 1500
Supported by vehicle data
Software updates for 2022 trucks and an MGU connector bulletin for 2020-2021 trucks name P1C64. Whether the bulletins are still current is not verified.

08-093-22Status unverified
HCP software update for P1C64 autostart failure
20221500 · issued May 13, 2022 · NHTSA 10214603
P1C64 and U0402 with an autostart that fails and the transmission in limp mode: update the hybrid control processor software.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.
08-025-23Status unverified
HCP software update, P1C64 and U0402
20221500 · issued January 26, 2023 · NHTSA 10231802
Same concern and remedy as 08-093-22: P1C64 with U0402, autostart failing and AutoPark engaging; reflash the HCP.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.
08-014-21Status unverified
MGU connector not fully seated
2020–20211500 · issued January 27, 2021 · NHTSA 10187133
P1C64 with U0594, P1B03, P0A3F, P0607 or P0A92, a stall 15-40 minutes into driving and no restart: replace the motor generator unit.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.
9004484Status unverified
Document before replacing the MGU for noise or P1C64
2019–20221500 · issued May 4, 2022 · NHTSA 10214520
Dealers should create a scan report and call engineering before replacing an MGU for whining noise or P1C64.
We couldn't confirm whether this bulletin is still current, so it doesn't count as confirmation.

All Hybrid and electric drive codes

Sources and review

FCA 08-093-22: Flash: Hybrid Control Processor (HCP) Updates — FCA US / NHTSA , April 1, 2022
FCA 08-025-23: Flash: Hybrid Control Processor (HCP) Updates — FCA US / NHTSA
NHTSA complaint 11462915: 2021 Ram 1500 — NHTSA (owner complaint)
NHTSA complaint 11660434: 2022 Ram 1500 — NHTSA (owner complaint)
FCA 08-014-21: Motor Generator Unit (MGU) Connector Not Fully Seated — FCA US / NHTSA
FCA 9004484: Motor Generator Unit — FCA US / NHTSA
NHTSA complaint 11438272: 2021 Ram 1500 — NHTSA (owner complaint)
NHTSA complaint 11633592: 2022 Ram 1500 — NHTSA (owner complaint)

Last reviewed: October 16, 2026
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

Severity: Inspect soon

Pick your make

Most likely causes

Cause 1: Hybrid control processor software

Cause 2: Motor generator unit or its connector

What to test first

Step 1: Read stored, pending and permanent codes and save a scan report with freeze-frame data

Step 2: Ask a Ram dealer to check your VIN for open bulletins and software updates and to inspect the MGU connector before any part is replaced

Symptoms

How to fix

Parts and cost context

On your vehicle

RamYour car

Related codes

Sources and review

Ram