P1621 on 2007-2009 Saturn Aura: Transmission Control Module Memory Failure

What's Unique About the 2007-2009 Saturn AURA

While P1621 is a general GM memory fault code, on the Saturn Aura and its platform mates (like the Chevy Malibu and Pontiac G6) using the 6-speed 6T70 automatic transmission, it is strongly associated with the Transmission Control Module (TCM). This module, often called a TEHCM (Transmission Electro-Hydraulic Control Module), is located inside the transmission, bolted to the valve body. This internal location subjects it to constant, intense heat and vibration, leading to a high failure rate. Technical Service Bulletin #PIP4653E specifically directs technicians to investigate the TCM when this code appears. The issue is common enough that many specialists offer pre-programmed or cloned replacement TCMs for this specific vehicle.

Diagnostic Flowchart

Tap your situation to follow the diagnostic path that matches what you're seeing on this vehicle.

Symptoms You May Notice

• Check Engine Light is on
• Transmission may shift harshly or erratically
• Vehicle may get stuck in one gear (limp mode)
• Delayed engagement when shifting into Drive or Reverse
• Loss of Reverse gear entirely
• Hesitation or bucking during acceleration
• Gear position indicator (PRNDL) on the dash is blank or incorrect
• In some cases, complete loss of communication with the TCM 🎬 Watch: Real-world examples of Saturn Aura transmission issues, which may set a U0101 code

Most Likely Causes

1. Internal Transmission Control Module (TCM/TEHCM) Failure 🔴 High Probability The TCM on these models, known as a TEHCM, is a known failure point. Its location inside the transmission pan subjects it to constant heat cycles and vibration, which can lead to the degradation of internal electronic components, solder joints, and memory chips, causing this specific fault code. TSB #PIP4653E directly links P1621 to the TCM.
   How to confirm: After confirming battery voltage and wiring are good, a professional scan tool is used to communicate with the TCM. If the code returns immediately after clearing, if the module fails to reprogram, or if it fails to communicate at all, it is condemned.
   Typical fix: Replace the Transmission Electro-Hydraulic Control Module (TEHCM) and program the new unit to the vehicle's VIN using GM's Service Programming System (SPS).
   Est. part cost: $250-$550
2. Low or Unstable Battery Voltage ⚪ Low Probability
   How to confirm: Test the battery and charging system. A battery resting below 12.4 volts or a charging voltage outside the 13.7-14.7 volt range indicates a problem. TSB #05-06-04-060A specifically advises repairing any low voltage conditions before diagnosing memory codes. Ensure battery terminals are clean and tight.
   Typical fix: Recharge or replace the battery. Repair the charging system if necessary.
   Est. part cost: $150-$300
3. Poor Electrical Connections to TCM ⚪ Low Probability The main transmission harness connector on the side of the transmission case can be susceptible to corrosion or damage, leading to intermittent power, ground, or data signal loss to the internal TCM.
   How to confirm: Visually inspect the main transmission wiring harness and connector for corrosion, damage, or loose pins. Check for proper voltage and ground at the connector using a multimeter and wiring diagram before condemning the internal module.
   Typical fix: Clean, repair, or replace the damaged wiring or external connector.
   Est. part cost: $20-$150

Rare But Worth Checking

• Corrupted TCM Software:

Diagnosis Steps

1. Verify the P1621 code is present using a professional-grade OBD-II scanner capable of reading codes from the Transmission Control Module.
2. Check for other related codes, especially P0700, P0601, P0603, P0604, or U0101, as noted in TSBs #05-06-04-060A and #PIP4653E.
3. Test the vehicle's battery and charging system to ensure stable voltage above 12.4V at rest and between 13.7-14.7V when running. Correct any voltage issues first.
4. Inspect the main external TCM connector and wiring harness for any signs of corrosion, water intrusion, or physical damage.
5. Using a wiring diagram, verify that the TCM is receiving proper power and has a solid ground connection at the external connector. Pay attention to ground G107, located at the right front of the engine.
6. If power, ground, and wiring are confirmed to be good, the fault is almost certainly internal to the TCM/TEHCM.
7. As a final diagnostic step, attempt to re-flash/reprogram the existing TCM. If the procedure fails or the code immediately returns, the TCM must be replaced.
8. Install a new or remanufactured TEHCM, new gaskets, and fresh DEXRON-VI fluid. Program the new module to the vehicle's VIN using the appropriate manufacturer software (GM SPS). Perform the 'Service Fast Learn Adapts' procedure after programming.

Parts You'll Likely Need

• Transmission Control Module (TCM/TEHCM) (OEM #24252114) — This is the control unit that fails internally, causing the P1621 memory performance error. On the Saturn Aura with the 6T70 transmission, this module (TEHCM) is inside the transmission and is the primary point of failure. The original part number 24252114 has been superseded by other numbers; always verify the correct part by VIN before ordering.
  Trusted brands: ACDelco (OEM), Dorman (e.g., 609-000), Standard Ignition
  OEM price range: $400-$600
  Aftermarket price range: $250-$450
• Transmission Pan Gasket and Fluid — Since the TEHCM is located inside the transmission, the side pan must be removed for access. 🎬 Watch: How to access the valve body without removing the transmission This requires draining the fluid and replacing the gasket upon reassembly. Only DEXRON-VI fluid should be used.
  Trusted brands: ACDelco, Fel-Pro, Valvoline, Castrol
  OEM price range: $80-$150
  Aftermarket price range: $50-$100

Related Codes That Often Appear With This One

• P0700 — P0700 is a generic code that means the TCM has stored a fault. It is set by the ECM to illuminate the check engine light and often appears alongside more specific TCM codes like P1621.
• P0601 — This code also indicates a control module memory error ('Internal Control Module Memory Check Sum Error'). Seeing it with P1621 reinforces the diagnosis of a failed module, and both are mentioned in TSB #PIP4653E.
• P0604 — This code means 'Internal Control Module Random Access Memory (RAM) Performance'. Like P0601, its presence strongly suggests the control module itself has failed and is also listed in TSB #PIP4653E.
• U0101 — This code means 'Lost Communication With TCM'. It can appear if the TCM has failed completely and is no longer responsive on the vehicle's data network.

Technical Service Bulletins (TSBs) & Recalls

• PIP4653E: Advises technicians that DTCs P0601, P0603, P0604, P062F or P1621 stored in the Transmission Control Module are indicators of an internal module fault.
• 05-06-04-060A: Communicates that P1621 is one of several control module memory codes that can appear in multiple modules, and that any low voltage conditions should be addressed before further diagnosis.

Platform-Specific Known Issues

• The Saturn Aura is specifically mentioned in GM Technical Service Bulletin #PIP4653E regarding DTCs like P1621 being stored in the Transmission Control Module (TCM).
• Another TSB, #05-06-04-060A, notes that P1621 is one of several control module diagnostic codes that can be set across multiple different modules, but experience on this platform points overwhelmingly to the TCM.
• The 6T70 transmission in the Aura is also known for a separate mechanical issue: a broken 3-5-R wave plate, which can cause similar shifting symptoms but is a different failure. A proper diagnosis is needed to distinguish between the electronic TCM failure (P1621) and the mechanical wave plate failure.
• The TCM is integrated with the valve body solenoids and pressure switches into a single unit called a TEHCM, which is located inside the transmission pan, bolted to the valve body. This location is the primary reason for its heat-related failures.

Mechanic-Grade Diagnostic Values

• Battery Voltage (Key-On, Engine-Off) — expected: >12.4 Volts. Failure: A reading below 12.4V indicates a discharged or failing battery that can cause spurious module codes.
• Charging System Voltage (Engine Running) — expected: 13.7 - 14.7 Volts. Failure: Voltage outside this range indicates a problem with the alternator or voltage regulator.
• CAN Bus Signal Voltage (at DLC or TCM connector) — expected: Approx. 2.5 Volts DC square wave (back-probed). Failure: No signal or a signal shorted to ground or power indicates a communication network problem.

Scan Tool Commands That Help

• GM MDI2 with Techline Connect: Service Programming System (SPS) — This is required to load the correct firmware and vehicle's VIN into a new TEHCM. The vehicle will not operate correctly without this step.
• GM Tech 2 or Professional Scan Tool: Service Fast Learn Adapts — This procedure must be performed after installing and programming a new TEHCM to allow the module to quickly learn clutch fill times and pressure characteristics for smooth shifting.

Wiring & Ground Locations

• G107 — Located on the right front of the engine.. This is a primary ground point for the engine and transmission control systems. A loose or corroded connection here can cause intermittent power loss or unstable voltage to the TCM, potentially triggering memory codes like P1621.
• Main Transmission Harness Connector — The large, multi-pin connector on the side of the transmission case where the vehicle harness connects to the internal TEHCM.. This is the single point of failure for all power, ground, and data communication to the TEHCM. It is exposed to the elements and can suffer from corrosion, fluid intrusion, or loose pins, mimicking an internal module failure.

Real Owner Repair Stories

• Reddit user cabo169, r/chevymalibu (2016 Chevy Malibu LT (platform mate with similar transmission architecture)) — Transmission locked in 3rd gear (safe mode). Scan showed BCM and PCM not communicating with TCM.
  ❌ Tried (didn't work) Owner was quoted $5,350 for a used transmission or $8,000 for a new one by a shop that was unsure if a TCM replacement would fix it.
  ✅ What actually fixed it The community advised that the symptoms pointed directly to a failed TCM, not a mechanical transmission failure, and that the shop was likely trying to upsell a much larger job. The correct, and much cheaper, repair was to replace only the TCM for the quoted $2,300. This highlights a common misdiagnosis where the entire transmission is condemned for a purely electronic fault.

OEM Part Supersession History

• 24234503 → 24239224, then 24252114 — Standard part evolution and revision by the manufacturer.
  Heads up: While these part numbers are linked, fitment for the 6T70 TEHCM is extremely specific. Multiple visually identical but internally different versions exist. Always confirm the correct part number for your specific vehicle by VIN before ordering.

Model Year Variations Within This Range

• 2007-2009: The P1621 TEHCM failure is specific to models equipped with the 6-speed 6T70 automatic transmission. In 2007, this was primarily the uplevel Aura XR with the 3.6L V6. Base XE models in 2007 used a 3.5L V6 with a 4-speed 4T45-E automatic, which does not have this specific TEHCM issue. For 2008-2009, a 2.4L 4-cylinder was introduced, which used either the 4-speed or a different 6-speed (6T40), while the 3.6L V6 with the 6T70 remained the application prone to this failure.