P26A2

Code

Generic P — Powertrain

Exhaust Aftertreatment Glow Plug Circuit High

Brand: Generic

Type: P — Powertrain

Views: UK: 26 EN: 52 RU: 25

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Page language: EN

Short to battery voltage in EAT glow plug wiring
Faulty exhaust aftertreatment glow plug module or heater element
Failed control relay or power supply for the glow plug circuit
Corroded/loose connector or damaged wiring harness (chafing, pinched, water intrusion)
Faulty engine control / aftertreatment control module
Incorrect replacement part or installation error

Malfunction Indicator Lamp (MIL) illuminated
Reduced or failed aftertreatment heating function (extended DPF regen times or regen fail messages)
Possible poor cold-start behavior on some systems
Stored/active DTC(s) related to aftertreatment heating

Retrieve freeze frame and all stored DTCs with a scan tool and note freeze-frame data and PID values
Visually inspect connectors, wiring harness, and ground connections for the EAT glow plug module for corrosion, heat damage or chafing
Check fuses and relays related to the glow plug/aftertreatment heater circuit
With key on (engine off) monitor battery voltage at the glow plug power supply connector
Use a multimeter to measure voltage at the control/command pin when the heater is commanded ON by the scan tool
Measure resistance of each heater element and compare to manufacturer specification (see notes)

Activation voltage: approximately battery voltage when commanded ON (use manufacturer spec; typically 12 V or 24 V systems)
Heater element resistance: low ohms per element (check vehicle-specific specification)
Current draw: high amperage relative to other low-voltage circuits; expect several amps per heater element — compare with factory spec
Control signal: PCM/ACM/aftertreatment module will command the circuit on; monitor command PID and power rail separately

Connect a calibrated scan tool and note freeze-frame data and related DTCs. Attempt to command EAT heaters ON while monitoring PIDs.
Perform a visual inspection of connectors, harness routing, and grounds for the EAT glow plugs and control module. Repair any obvious damage or corrosion.
Check fuses and relays for the heater power supply. Replace faulty items and retest.
With ignition ON (engine OFF) and command active, measure the voltage at the heater power feed. If voltage is above battery voltage or unstable, inspect power supply and regulator circuits.
Measure resistance of each heater element (with battery disconnected). Compare to factory values. Very low or near-zero ohms indicates internal short; very high or open indicates open circuit.
If resistance and power feed appear normal, use a clamp ammeter to measure current draw while commanded ON. Excessive current indicates internal shorted element or harness short.
If wiring and heaters test OK, backprobe the control module output and check for short to voltage in wiring between module and heaters. Repair or replace damaged wiring as needed.
If wiring and heaters are good and the power rail/relay are operating correctly, suspect control module fault. Verify with manufacturer-specific diagnostics before replacing module.
After repairs, clear codes, perform forced regen or heater activation cycle if required, and verify the DTC does not return during drive/operation. Record results and retest as needed.

⚠️ Status

P26A2 — Exhaust Aftertreatment Glow Plug Circuit High (over-voltage/over-current or short-to-voltage detected)

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-3.0 hours

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