Range/performance fault of transmission fluid pressure sensor or switch E: the signal is electrically valid but does not fit the commanded clutch state or the pressure expected from other inputs. No manufacturer documents this code publicly. GM's 6T70/6T75 family, the one public user of switch E (switch 5 on the low/reverse and 4-5-6 regulator valve), folds such plausibility checks into P0989 and P0990; its switch logic table shows which gears should pressurise the switch. Sonnax describes how these normally closed film switches in the valve body module fail through debris or delaminated films. CARB requires rationality checks of transmission inputs. Siblings: P0987 circuit, P0989 low, P0990 high.
Medium severity. Can I keep driving?Drive gently to a repair shop. If it slips, you hear clunks, or it loses its gears, do not keep driving.
Symptoms
- Often no noticeable symptom at first
- Shift quality worsens because adaptation stops
- Warning light depending on manufacturer
Most likely causes
- Damaged or delaminated switch film, switch reacts late or not at all
- Debris in the fluid holding the switch or its regulator valve
- Low fluid level or real pressure deviation in the clutch circuit
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: hard
- It can trigger limp mode.
- It affects emissions.
What each character of P0988 means
- P: Powertrain: engine and transmission
- 0: Generic code: same on every make
- 9: Transmission
- 88: Specific fault in that system
Frequently asked questions
Can I keep driving with code P0988?
Drive gently to a repair shop. If it slips, you hear clunks, or it loses its gears, do not keep driving.
What causes code P0988?
The most common causes are: damaged or delaminated switch film, switch reacts late or not at all; debris in the fluid holding the switch or its regulator valve; low fluid level or real pressure deviation in the clutch circuit.
Related codes
- P0987Transmission Fluid Pressure Sensor/Switch E Circuit
- P0989Transmission Fluid Pressure Sensor/Switch E Circuit Low
- P0990Transmission Fluid Pressure Sensor/Switch E Circuit High
- P0871Transmission Fluid Pressure Sensor/Switch C Circuit Range/Performance
- P0876Transmission Fluid Pressure Sensor/Switch D Circuit Range/Performance
- P0993Transmission Fluid Pressure Sensor/Switch F Circuit Range/Performance
Sources
- law.cornell.edu: 13 CCR 1968.2
- saabwisonline.com: transmission fluid pressure switch logic
- sonnax.com: 215 under pressure shift quality pressure switches
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.