P0263: Cylinder 1 Contribution/Balance Fault - Causes, Fixes & Cost [2026]
What is P0263? P0263 is set when the PCM compares the crankshaft acceleration after each cylinder firing event and finds cylinder 1 contributes less than the others by more than the calibrated threshold. Causes range from a weak injector to low compression or a bad spark plug.
🎯 Top 3 Causes Ranked by Probability
45%
#1 - Most Likely
Weak or Partially Clogged Injector
Cyl 1 injector is dribbling or flowing less than the others. Cleaning or replacement fixes it.
🔨 Part
$80-$500
👨🔧 Labor
$100-$350
⚡ DIY
Medium
30%
#2 - Check First
Low Compression on Cyl 1
Worn rings, burnt valve, or a stretched timing chain has dropped cyl 1 compression. A compression test confirms.
🔨 Part
$200-$2000
👨🔧 Labor
$400-$1500
⚡ DIY
Hard
25%
#3 - Less Common
Bad Spark Plug or Coil (gas engines)
Worn plug or weak coil drops cyl 1 output without setting a misfire code. Quick to test by swapping with another cylinder.
🔨 Part
$15-$120
👨🔧 Labor
$50-$200
⚡ DIY
Easy
🔧 Step-by-Step Diagnosis
- Run a compression test on cyl 1 and compare to the other cylinders. Spec is usually 130-180 psi with no more than 10% variance.
- On gas engines, swap the cyl 1 plug and coil with cyl 2 and clear the code. If the fault moves to cyl 2, the ignition part is at fault.
- On diesels, run injector balance test through a scan tool. The PCM reports per-cylinder fuel correction - cyl 1 will stand out.
- Clean or replace the cyl 1 injector if balance is more than 3-5 mg off the average.
- If compression, ignition, and injection all check good, inspect the cyl 1 valves with a borescope.
🚗 Most Affected Vehicles
🚫 Is It Safe to Drive with P0263?
Short term yes, but driveability is poor and emissions are elevated. Fix soon to avoid catalyst damage.
❓ Frequently Asked Questions
What does a cylinder balance fault mean?
The PCM measures how much each cylinder accelerates the crankshaft and flags any cylinder that lags behind. P0263 means cyl 1 is the weak one.
Is P0263 the same as a misfire?
Not exactly. A misfire is no combustion at all; P0263 is partial combustion that still fires but produces less power.
Can dirty injectors cause P0263?
Yes, this is one of the most common causes. A professional cleaning or a high-quality fuel system cleaner can solve it on early-stage cases.
How do I test injector balance?
Most modern scan tools support an injector balance test that disables each injector in turn and reports the RPM drop. Big differences point to the weak cylinder.
Will P0263 cause a check engine light?
Yes. Cylinder balance is part of the misfire monitor and a confirmed P0263 illuminates the MIL.