P0128 on Cadillac Lyriq: Fix & DLC Location
Factory diagnostic troubleshooting wire for fault code P0128 (P0128: Coolant Temperature Below Thermostat Regulating Temperature) specifically on the Cadillac Lyriq (2023–2026, Ultium Dual Motor AWD (500HP / 450 lb-ft) / Single Motor RWD (340HP)).
1. Symptoms of P0128 on Cadillac Lyriq
When the Engine Control Module (ECM/PCM) on your Cadillac Lyriq (Ultium Dual Motor AWD (500HP / 450 lb-ft) / Single Motor RWD (340HP)) logs fault code P0128, drivers commonly observe:
2. Most Likely Causes on Cadillac Lyriq
Historical warranty claims and technical repair bulletins for Cadillac Lyriq point to the following failure distribution:
3. Step-by-Step DIY Repair Guide for Cadillac Lyriq
Ensure coolant is topped up when engine is completely cold. on the Cadillac Lyriq equipped with Ultium Dual Motor AWD (500HP / 450 lb-ft) / Single Motor RWD (340HP).
Read live coolant temp; should reach 195°F-215°F within 10 minutes. on the Cadillac Lyriq equipped with Ultium Dual Motor AWD (500HP / 450 lb-ft) / Single Motor RWD (340HP).
Drain 1 gallon coolant, unbolt thermostat housing, install new OEM thermostat with jiggle valve up. on the Cadillac Lyriq equipped with Ultium Dual Motor AWD (500HP / 450 lb-ft) / Single Motor RWD (340HP).
Use spill-free funnel to burp air bubbles out of the heater core and engine block. on the Cadillac Lyriq equipped with Ultium Dual Motor AWD (500HP / 450 lb-ft) / Single Motor RWD (340HP).
Clear codes and confirm heater blows 130°F+ hot air at idle. on the Cadillac Lyriq equipped with Ultium Dual Motor AWD (500HP / 450 lb-ft) / Single Motor RWD (340HP).
Other Common Fault Codes on Cadillac Lyriq
Frequently diagnosed powertrain, emissions, and sensor trouble codes logged on the Cadillac Lyriq:
4. Cadillac Lyriq P0128 FAQs
What causes code P0128 to trigger on a Cadillac Lyriq?
On the Cadillac Lyriq (Ultium Dual Motor AWD (500HP / 450 lb-ft) / Single Motor RWD (340HP)), P0128 is most frequently caused by Thermostat stuck open or Faulty Engine Coolant Temperature (ECT) sensor.
Where is the OBD-II port located on my Cadillac Lyriq?
On the Cadillac Lyriq, the 16-pin DLC diagnostic connector is located Under driver steering column beneath knee bolster. Plug in any standard OBD-II scanner with the ignition in the ON position to read freeze-frame parameters.
Can I safely drive my Cadillac Lyriq with code P0128?
Yes, but heater may blow lukewarm and fuel mileage will drop. Given that P0128 carries a Low severity rating, we advise avoiding heavy towing or aggressive throttle inputs until sensor readings are verified.