2021 Jeep Wrangler PCM Update for MIL and DTCs

Owners of the 2021 Jeep Wrangler equipped with the 3.6L V6 VVT Engine Upgrade 1 (Sales Code ERC) may experience various issues, including the illumination of the Malfunction Indicator Lamp (MIL) and specific Diagnostic Trouble Codes (DTCs). Technical Service Bulletin (TSB) 18-005-26, dated January 29, 2026, addresses these concerns by providing a software update for the Powertrain Control Module (PCM). This Jeep Wrangler PCM update aims to resolve these problems and improve overall vehicle performance.

This bulletin supersedes a previous version, TSB 18-041-22 REV. A, which was issued on March 19, 2022. The current revision, 18-041-22 REV. A, includes new DTCs and customer symptoms, an updated diagnosis statement, and revised repair procedures.

Symptoms

Customers may notice a Malfunction Indicator Lamp (MIL) illumination on their dashboard. In addition to the MIL, several other symptoms might indicate the need for this Jeep Wrangler PCM update:

• The vehicle may enter "limp home mode."
• A "Service Transmission" message might appear in the Instrument Panel Cluster (IPC) due to clutch slip detection, particularly in manual transmission vehicles. This can occur if the PCM interprets wheel spin or slippage as excessive clutch slip, leading to the message to prevent clutch damage.
• The engine might produce a "Spark knock/detonation" sound, especially when idling.

Other software enhancements included in this update improve valvetrain component reliability by enabling the engine oil pump to operate in high-pressure mode with cold engine oil.

Fault Codes / DTCs

If the Malfunction Indicator Lamp (MIL) is illuminated, a scan tool may reveal one or more of the following Diagnostic Trouble Codes (DTCs):

• P08A6 – Gear Lever Position Sensor System – Multiple Sensor Correlation (for manual transmission vehicles in North America only).
• P152F – Engine Hood Switch 2 / Engine Hood Switch 1 Correlation (for North America only).
• P0300 – Multiple Cylinder Misfire.

Diagnosis

To diagnose these issues, technicians should use a wiTECH scan tool. This tool allows for the verification of all related systems and appropriate diagnostic procedures available in DealerCONNECT/Service Library. If any DTCs or symptoms other than those listed in this bulletin are present, they should be recorded and addressed before proceeding with the PCM reprogramming. If the customer's reported symptoms match those described in this bulletin, the repair procedure can be initiated.

Repair Procedure Summary

The core of the repair involves reprogramming the Powertrain Control Module (PCM) with the latest available software. This process requires specific steps to ensure a successful update:

1. Prepare the Vehicle: Install a battery charger to maintain the battery voltage between 13.2 and 13.5 volts throughout the flash process. It is crucial not to let the voltage drop below 13.2 volts or climb above 13.5 volts.
2. PCM Reprogramming: Reprogram the PCM using the wiTECH Diagnostic Application. If any issues arise during the flashing process, technicians should submit a ticket to the Helpdesk through the Help menu.
3. Clear DTCs: After the reprogramming is complete, clear all Diagnostic Trouble Codes (DTCs) that may have been set in any module. The wiTECH application will automatically present all DTCs for clearing.

Required Tools or Parts

• wiTECH or Equivalent: A compatible scan tool is necessary for diagnosing the issue and performing the PCM reprogramming.
• Battery Charger: A stable power supply is critical to maintain battery voltage during the software flash process.

Important Warnings

• If the PCM flash process is interrupted or aborted for any reason, it must be restarted from the beginning.
• After applying TSB 18-005-26, it is explicitly stated that it is not necessary to send DID-I or DID-A. This is an important note for technicians regarding post-repair documentation.

Owner Action

If your 2021 Jeep Wrangler exhibits any of the symptoms described, such as a Malfunction Indicator Lamp illumination, a "Service Transmission" message, or engine performance issues like spark knock, it is recommended to visit an authorized Jeep dealership. The Jeep Wrangler PCM update is reimbursable under warranty provisions. The repair typically takes about 0.3 hours of labor time.

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Source: NHTSA ID: 11028232