Transmission control module (TCM) codes

The TCM runs an automatic transmission: it reads sensors and controls shifting and torque converter lockup. When it finds a fault that affects emissions it asks the engine computer to turn on the check engine light, which is what P0700 reports.

How its codes differ

  • P0700 does not identify the fault: it only says the TCM has a code stored. The detail is in the TCM's own codes, which need a scan tool that can talk to the transmission module.
  • P0741 is one of the specific faults that can sit behind P0700: the torque converter clutch is not locking up as commanded or slips.
  • A TCM fault code does not by itself mean the module is bad: sensors, solenoids, wiring or fluid problems inside the transmission are more often what the TCM is reporting. GM has a bulletin for P0700 set in the TCM on some low-mileage vehicles.

Codes

  • P0700

    Transmission module requests the check engine light

    Inspect soon

  • P0741

    Torque converter clutch not engaging as commanded

    Inspect soon

Signs it's failing

  • Check engine light with P0700
  • Harsh, delayed or missing shifts
  • Transmission indicator flashing on some vehicles
  • Limited performance from a fail-safe mode

How to test it

  1. Read the transmission module's own codes with a scan tool that supports it; P0700 alone is not enough to diagnose anything. (Low risk)

  2. Check for service bulletins and recalls for your vehicle. (Low risk)

  3. Transmission diagnosis and module programming or replacement are shop jobs. (Best left to a shop)

    Warning: Transmission faults can cause sudden loss of drive or harsh shifts; if shifting changes, avoid hard acceleration and have it checked promptly rather than testing it on the road.

After the repair

  • Clear codes in both the engine and transmission modules and confirm none return after a drive with all gears.
  • Clear codes only after the repair, then drive normally over several days with both city and highway driving so the readiness monitors can complete; clearing codes or disconnecting the battery resets them to not ready, which fails an emissions test.

Sources and review

  1. DTC P0700 — Saab 9-5 (9650) 2010 Workshop Information System — SaabWISOnline (community rehost of Saab/GM service information)
  2. GM 23-NA-210: MIL with P18AE and/or P0700 set in the TCM on low-mileage vehicles — General Motors / NHTSA ,
  3. Honda owner's manual: Continuously Variable Transmission, shift lever position indicator (p. 166) — American Honda Motor Co. ,
  4. 2020 Nissan Altima Owner's Manual — Nissan North America
  5. Toyota Camry Owner's Manual (OM06291U, 2.5L A25A-FKS / 3.5L 2GR-FKS) — Toyota
  6. Final Regulation Order: 13 CCR §1968.2, Malfunction and Diagnostic System Requirements (OBD II), 2004 and subsequent model-year passenger cars, light-duty trucks and medium-duty vehicles (2015 amendments) — California Air Resources Board
  7. OBD Vehicle 'Readiness' Fact Sheet (E-Check) — Ohio Environmental Protection Agency
Last reviewed
Written by
Saurabh K.
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