P26A1: Exhaust Aftertreatment Glow Plug Circuit Low

What it means

The aftertreatment glow plug current is below expected. Either the element is partially open or supply is undersized.

At a glance

• Usually lights the check-engine light

How it works

The aftertreatment glow plug heats the exhaust on some diesels to help ignite fuel during DPF regeneration. P26A1 sets when measured glow plug current is below the expected level, which can mean a weakened element or excessive voltage drop in its supply or connector.

Common causes

Most likely first.

1. Partial element failure raises resistance
2. Supply voltage drops under load
3. Connector pins corroded - high contact resistance

Symptoms

• Glow plug warning light on (often orange coil symbol)
• Hard cold start or no start in cold weather
• White smoke from exhaust during warm-up

How to diagnose it

1. Review freeze-frame data and live current during a commanded glow plug event to confirm when the low-current condition occurs.
2. Inspect the glow plug connector and supply wiring for corrosion, loose pins, heat damage, or a weak connection.
3. Measure supply voltage at the plug under load and compare it with the manufacturer's specification to identify voltage drop.
4. With power isolated as specified, measure glow plug element resistance and compare it with the manufacturer's specification.
5. If the element and supply pass, check relay contacts and the upstream power and ground path under load.

Common fixes

• Clean and secure a serviceable corroded or loose connector.
• Repair a damaged supply wire or poor ground causing voltage drop.
• Replace the glow plug if its resistance or current remains below specification.
• Replace a relay with excessive contact resistance if the supply drops across it.

Can I keep driving?

If the engine runs normally, gentle driving may be possible, but cold starts can become difficult and regeneration may not complete. Avoid repeated short trips and address persistent white smoke or a DPF warning promptly.