OBD-II trouble code
P0882: TCM Power Input Signal Low
On a power input, "low" means the voltage really was low — not that a wire is shorted somewhere. That is the opposite of what the surrounding sensor codes mean by the same word, and getting it the wrong way round sends the whole diagnosis into the harness instead of the battery.
Quick facts
- System
- Powertrain
- Category
- Transmission / Electrical Supply
- Severity
- High severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $80 – $1,200
- DIY difficulty
- Advanced DIY
What does P0882 mean?
Start with the word "low", because it does not mean here what it means on the codes immediately below this one in the numbering, and that single misunderstanding is responsible for an enormous amount of wasted effort.
On a sensor circuit — a pressure sensor, a temperature sensor, a position sensor — "circuit low" is a statement about wiring. The module put out a reference voltage, expected the sensor to return some fraction of it, and instead saw the signal wire dragged down towards ground. The reading itself is meaningless; what the code describes is a wiring fault with a direction.
A power input is a completely different kind of circuit, and "low" on it is a statement about magnitude. The transmission control module is not interpreting a signal here. It is measuring the actual supply voltage arriving at its own power pin and reporting that the number was beneath the threshold it needs to operate reliably — typically somewhere around nine or ten volts, though manufacturers set it differently. Nothing is shorted to anything. The voltage genuinely was not there.
That reframing changes where you look first. It moves the battery, the charging system and the connections that carry current to the front of the list, and it pushes signal-wire diagnosis to the back where it belongs. It also explains why this code so often turns out to have a twenty dollar answer.
There is one population of vehicles that sets this code with nothing whatsoever wrong with them, and it is worth ruling out before touching a tool. Vehicles that sit — seasonal cars, a second vehicle used twice a month, fleet spares, anything that has spent weeks on a forecourt — accumulate a slow discharge from the modules that stay partly awake, the alarm, the keyless entry receiver and the clock. When such a vehicle is finally started, cranking pulls an already depleted battery well below the module's threshold and the code is set honestly, describing exactly what happened. If the vehicle then drives normally for a fortnight and the code does not return, there was never a component fault; there was a usage pattern. The distinguishing question is not technical, it is simply whether the car gets driven, and asking it costs nothing.
The more important reason to take the order of operations seriously is financial, and it protects the owner rather than the workshop. A control module being fed insufficient voltage does not behave like a module with a power problem. It behaves like a module that has failed. It drops communication, gives nonsensical readings, makes poor decisions, sets unrelated internal faults and generally presents every symptom of hardware that has died. A scan tool cannot distinguish between the two states from the outside, and neither can a technician working quickly. That is precisely how a replacement transmission control module gets fitted, programmed and invoiced against a fault that was a corroded battery terminal — and how the same symptoms reappear a fortnight later with a new module in the car. Proving the supply first is not diagnostic pedantry. It is the step that stands between the customer and a bill an order of magnitude larger than the problem deserved.
Common causes
- Discharged or weak battery, including one flattened by the vehicle standing unused
- Parasitic current draw discharging the battery between journeys
- Failing battery cell or high internal resistance limiting available voltage
- Corroded, loose or under-torqued battery terminal clamps
- Charging system not restoring the battery, so supply voltage never recovers
- Corroded or high-resistance ground connection at the module or body
- Undersized or damaged power feed wire dropping voltage along its length
- Poor connection at a fuse box junction or power distribution block
- Extended cranking on a marginal starter pulling supply below the threshold at every start
- Internal transmission control module fault, which should only be considered once the supply is proven
Symptoms
- Check engine light with P0882 stored
- Transmission holding a fixed gear or entering fail-safe operation
- Delayed or harsh engagement when selecting drive or reverse
- Slow cranking, or the code appearing only after the vehicle has stood for a while
- Battery repeatedly requiring a jump start or a charger
- Scan tool unable to establish or hold communication with the transmission controller
- Several modules reporting low-voltage faults during the same key cycle
- Dash warning lamps flickering on and off during starting
- Symptoms clearing entirely after the battery is charged, then returning after the car stands again
- Radio presets, clock or seat memory lost, indicating the whole vehicle has been down on voltage
Diagnostic steps
- 1.Ask how often the vehicle is driven before anything else. A car that stands for weeks can set this code honestly with no component fault at all.
- 2.Measure resting battery voltage after the vehicle has sat for several hours, then load test the battery and check its state of health rather than just its charge.
- 3.If the battery is repeatedly flat, measure parasitic draw with the modules asleep and compare it against the manufacturer's allowance.
- 4.Confirm the charging system is actually restoring the battery, measuring output at idle and at raised engine speed.
- 5.Clean and torque the battery terminals and check the clamp and post for corrosion under the clamp face, where it is invisible.
- 6.Compare the voltage the scan tool reports at the transmission controller against the voltage measured directly at the battery. A meaningful gap between the two localises the loss.
- 7.Inspect and clean the module's ground connection, then confirm it with a measurement rather than by appearance.
- 8.Check every fuse and fusible link in the supply path, and inspect the fuse box sockets for heat discolouration.
- 9.Prove the supply is good before authorising a control module. A module starved of voltage presents exactly like a failed one, and replacing it does not fix the supply.
- 10.Verify the repair by monitoring module supply voltage through a cold start and a full drive cycle, not by clearing the code and hoping.
Repair cost
$80 – $1,200
The distribution of outcomes on this code is heavily weighted towards the cheap end. Cleaning and re-torquing battery terminals, or replacing a corroded clamp, is $80 to $200 including the diagnostic time. A battery is $150 to $400 fitted, and on a vehicle that simply stands unused, a charger and a change of habit may cost nothing at all. Tracing and repairing a parasitic drain is $120 to $350 depending on how long the hunt takes. An alternator is $400 to $900. Repairing a corroded ground or a damaged feed wire is $150 to $500. Replacing the transmission control module with programming is $500 to $1,200, and on this code in particular it should be the very last thing on the list — a module fed insufficient voltage is indistinguishable from a failed one, so a supply fault diagnosed hastily produces an expensive replacement that changes nothing.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with battery replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an advanced DIY job. It typically requires specialty tools, scan-tool access, lifting equipment, or careful sequencing to avoid causing new failures. Plan for extended downtime and have a backup vehicle. Most owners are better served by a shop that has done this repair before.