P0117 on Cadillac: How to Diagnose & Fix
Engine Coolant Temperature Sensor Circuit Low
1 Cadillac model · 1 documented issue · 1 critical · $2,000-$4,500 repair
P0117 on Cadillac by model: symptoms, diagnosis and fix
The Northstar 4.6L V8 in the DTS (and predecessor DeVille) has a well-documented design flaw where the aluminum block head bolt threads strip out, causing head gasket failure. The head gasket itself does not fail; instead the head bolts lose clamping force as the threads pull from the soft aluminum block. The problem is most severe on 1996-2003 engines. GM improved the bolt design in 2000 (longer bolts) and again in 2004 (coarser thread pitch). The Time-Sert thread repair is the accepted permanent fix.
Common Symptoms
- Unexplained coolant loss
- Overheating with no visible external leak
- White exhaust smoke (coolant burning)
- Oil contamination with coolant (milky residue)
- Exhaust gases in coolant reservoir (bubbling)
How to Fix
Confirm the failure with a block-combustion gas test, cooling-system pressure test, and by checking for repeated overheating/coolant loss with no external leak; on Northstar engines, a positive test usually indicates pulled head-bolt threads rather than a simple gasket defect. The permanent repair is to remove the powertrain, pull both cylinder heads, inspect for warpage/cracks, and install steel thread inserts in all head-bolt holes in the block (Time-Sert is the standard repair; some shops use NS300L/Big-Sert style kits on damaged holes), then reassemble with new head gaskets, new torque-to-yield head bolts, fresh coolant, and related seals. Simply replacing the head gaskets without inserting the block threads will usually fail again. Typical shop cost is about $3,500-$6,500 depending on engine condition and whether additional machine work, inserts, water pump, or crossover/case-half resealing is needed.
Sources for this issue (1)
P0117 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0117 mean on a Cadillac?
P0117 stands for "Engine Coolant Temperature Sensor Circuit Low." This code means the engine coolant temperature (ECT) sensor is reading too low a voltage, which the computer interprets as an impossibly high coolant temperature. In most cases this is an electrical fault — such as a short to ground in the wiring — rather than the engine actually overheating. The coolant temperature signal affects fuel mixture, cooling fans, and other functions, so a bad reading can cause poor running, hard starting, or fans running constantly. The fault is usually in the sensor or its wiring. On Cadillac it is documented across 1 model: DTS.
What are the most common causes of P0117?
The most common causes of P0117 are: Faulty engine coolant temperature sensor, Short to ground in the sensor signal wire, Damaged or corroded wiring/connector at the sensor, Coolant contamination affecting the sensor, Poor electrical ground, Faulty PCM/ECM (less common). The specific cause varies by vehicle.
How much does it cost to fix P0117 on a Cadillac?
Published repair estimates on Cadillac range from $2,000 to $4,500 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for P0117 on a different make?
View P0117 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.