P0978Generic code

P0978 Code: Shift Solenoid C Control Circuit Range/Performance

The P0978 code means the control circuit of shift solenoid C is outside its working range. Inspect the gearbox connector and wiring before replacing the solenoid. A multimeter may find nothing wrong, so compare what the solenoid does with what it was ordered to do.

Severity
High
Can I keep driving?
Yes, but with caution
Estimated cost
$80 to $900
Difficulty
Medium
System
Transmission
Applies to
All OBD2 vehicles

Updated Reviewed by Renzo Chacca

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What the P0978 code means

Solenoids are electric valves that send oil pressure to the clutches and brakes inside the gearbox. Shift solenoid C opens or closes the oil passage to one particular clutch, and the combination of solenoids decides which gear you are in. The transmission computer turns the solenoids on and monitors both their electrical circuit and the result (the input and output shaft speeds of the gearbox).

The P0978 code means the control circuit of the solenoid is outside its working range. It is an electrical fault, and the suspects are the wiring, the connector (very often the pass-through connector on the case, which leaks oil), the solenoid itself or the control module.

On any gearbox code, the first check is the oil: the right level using the manufacturer procedure (often with the engine running and at a set temperature), a red or pink color and no burnt smell. Low or degraded oil causes slipping, harsh shifts and solenoid or gear-ratio codes that disappear when it is corrected.

This kind of fault usually does not show up with a multimeter, because everything looks fine electrically. You have to compare what the part reports with reality: use a gauge, a thermometer or a tachometer, or command the component with the scan tool and see whether the physical result matches the order.

See our P0700 guide to understand how gearbox codes are read and why you need a scan tool that can reach the transmission module.

P0978 code symptoms

  • Check engine light or transmission light on.
  • Shifts that are harsh, late or do not happen.
  • Limp mode: the gearbox stays in a fixed gear (often 2nd, 3rd or 4th).
  • Slipping or high rpm in certain gears.

Likely causes of the P0978 code

  1. Gearbox connector with oil or corrosion. Very common on the pass-through connector on the case.
  2. Internal or external wiring damaged by heat or rubbing.
  3. Solenoid with an open or shorted coil. Its resistance is out of specification.
  4. Transmission control module. Uncommon.

How to diagnose the P0978 code step by step

  1. Check the oil level and condition using the manufacturer procedure.
  2. Read all the codes from the gearbox module with a scan tool that can reach it.
  3. Measure the solenoid resistance at the gearbox connector and compare it with the manual.
  4. Check the insulation to ground. It should read infinite.
  5. Command the solenoid with the scan tool and listen for the click.
  6. Inspect the case connector and look for oil inside it or green pins.

How to fix the P0978 code

  • Repair the connector or the wiring.
  • Replace the solenoid (or the valve body if the solenoid is built into it).
  • Clear the adaptations and do the relearn procedure.
  • Clear the P0978 code and verify with a road test.

Technical reference data

  • Shift solenoids (on/off): roughly 10 to 30 ohms.
  • Pressure or linear solenoids (PWM control): roughly 3 to 8 ohms.
  • Normal gearbox oil temperature: 70 to 95 °C (158 to 203 °F).
  • Reference values only: check the manufacturer data for your vehicle.

Brand-specific notes

In many gearboxes the solenoids live in the valve body and you reach them by taking off the pan. In some, the solenoids are sold only together with the valve body or with a built-in control module. After replacing solenoids or the valve body, you usually have to clear the adaptations and run a relearn with a scan tool.

P0978 on Aisin

On many Aisin gearboxes the solenoids sit in the valve body and are reached by removing the pan.

P0978 on Jatco

On many Jatco gearboxes the solenoids sit in the valve body and are reached by removing the pan.

P0978 on GM

On the GM 6T gearbox the solenoids sit in the valve body and are reached by removing the pan.

P0978 on Ford

On the Ford 6R gearbox the solenoids sit in the valve body and are reached by removing the pan.

P0978 on Volkswagen

The Volkswagen DSG uses a mechatronic unit, and in many modern gearboxes the solenoids come with the control module built in.

Frequently asked questions about P0978

Can I drive with a P0978 code?
With caution, and only as far as a shop. The gearbox can drop into limp mode, and running that way for a long time wears it out.
Will an oil change fix it?
Sometimes, mostly with performance or stuck-solenoid codes. A range code can be tied to oil condition, so check it before anything else.
Does the gearbox have to come out?
Normally not. Solenoids are changed by removing the pan or the valve body cover.
How much does it cost to fix P0978?
As a rough guide, between $80 and $900, and more if the gearbox itself needs repair.
What does the P0978 code mean?
It means the control circuit of shift solenoid C is working outside its expected range. It may look fine electrically while not giving the result the computer expects.
Will a P0978 code clear itself?
Only if the cause stops. A weak solenoid or a leaking connector will keep setting the code.

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