01 Mechanics Say This Common Driving Behavior Causes More Engi… • 02 Don't Get Stranded! A Guide to Roll Starting, Starters, and… • 03 You Could Destroy Your Entire Engine If You Keep Repeating … • 04 Mechanics Explain Shocking Reason Cars Overheat More Often … • 05 A Complete Guide To Diesel Particulate Filter (DPF) • 06 Types of Spanners: Uses, Advantages, and Material Compositi… • 07 This Is Why It’s Almost Impossible To Sink A Modern Cruise … • 08 Engineering Safety Matters: Promoting a Culture of Safety i… • 09 Top 7 Reasons Your Car Loses Power: Troubleshooting Common … • 10 Airbus and Boeing: The Battle of the Titans •

DTC codes / P08xx · Transmission / P0888

P0888TCM Power Relay Sense Circuit

P0888 indicates that the transmission control module (TCM) has detected a fault in the power relay sense circuit, which is the feedback line that confirms the relay is supplying voltage to the TCM. The TCM expects a specific voltage on this circuit when the relay is commanded on, and it sets this code when the signal is missing, erratic, or out of range.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaTransmission

Symptoms you may notice

  • Illumination of the check engine light or transmission warning light, often with no other symptoms
  • Transmission may enter limp mode, defaulting to a single gear or refusing to shift
  • Harsh or delayed shifting, or a complete loss of shift quality
  • The vehicle may fail to start or stall intermittently if the relay also powers other circuits
  • Erratic operation of the transmission, such as slipping or flaring between gears
  • No noticeable drivability issues besides the warning light in some cases

Common causes, most likely first

  1. Faulty transmission control module (TCM) power relay, such as worn contacts or a stuck coil
  2. Blown fuse or fusible link supplying power to the relay or TCM
  3. Corroded, loose, or damaged wiring or connectors in the relay sense circuit
  4. Poor ground connection for the relay or TCM, causing voltage drop
  5. Internal failure within the TCM affecting its ability to read the sense circuit
  6. Water intrusion or physical damage to the wiring harness near the relay or TCM

How to diagnose and fix it

  1. Verify battery voltage and inspect the fuse and relay box for blown fuses or a faulty relay
  2. Check the relay by swapping it with an identical known-good relay and clearing the code
  3. Perform a visual inspection of the relay sense circuit wiring and connectors for corrosion or damage
  4. Use a multimeter to measure voltage on the sense circuit with the key on and relay commanded on
  5. Check ground connections for the relay and TCM for resistance and tightness
  6. If the sense circuit is good, test the TCM's power and ground inputs and consider TCM replacement
  7. After repairs, clear codes and perform a road test to confirm the transmission operates correctly

Relay Sense Circuit Misdiagnosis Traps

  • A faulty relay is often replaced unnecessarily; the sense circuit itself can have high resistance from corroded terminals that mimic a failed relay.
  • The code can be set by a weak battery or charging system issue that causes voltage spikes or drops, so always check battery health first.
  • Some vehicles use the same relay to power multiple systems, so a failure may also cause unrelated electrical symptoms like radio or lighting issues.
  • The TCM may set this code intermittently if the relay coil is failing only when hot, so a cold-engine test may not reveal the fault.
  • Replacing the TCM without verifying the sense circuit voltage can lead to repeat failures if the underlying wiring fault remains.

Can I keep driving with P0888?

If the vehicle drives normally, you can drive it to a repair shop, but avoid heavy loads or long trips. If the transmission is in limp mode or shifting erratically, limit driving to a short distance to a safe location and seek professional diagnosis.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

Running on fumes Free guides aren't free to make. Top up the tank. Any amount, one time. Fuel the Garage