Code
P1198
RAM
P — Powertrain
Radiator Temperature Sensor Input voltage too high
AI status
Completed
Completed
100%
Causes
- Short to battery voltage on the sensor signal or reference circuit
- Faulty radiator/coolant temperature sensor (thermistor) with incorrect resistance
- Damaged, chafed, or corroded wiring or connector (pin corrosion, water intrusion)
- Poor or missing ground at PCM or sensor circuit
- Faulty PCM or internal input driver failure
- Aftermarket wiring or accessories tied into the temp signal or 12V feed
Symptoms
- Coolant temperature gauge may read unusually low or pegged
- Cooling fan operation abnormal (may run constantly or not run)
- Poor warm-up behavior or incorrect engine running until warm
- Illuminated Check Engine Light (MIL) with P1198 stored
- Possible reduced engine performance or limp-home mode on some vehicles
What to check
- Visually inspect sensor connector and wiring for damage, corrosion, or water
- Backprobe sensor signal and ground with engine off and key on; check for battery voltage and reference voltage
- Measure sensor resistance at known coolant temperature and compare to specification (service manual)
- Check PCM connector for bent pins, corrosion, or evidence of water
- Scan for additional related codes (ECT high/low/intermittent) and freeze frame data
- Wiggle test wiring while monitoring live data to reproduce voltage change
Signal parameters
- Typical coolant/radiator temp sensor signal expected: ~0.2–4.8 V (varies with temperature and vehicle)
- High-voltage fault generally set when signal exceeds ~4.8–5.0 V or above configured threshold
- Low-voltage / open condition generally below ~0.1–0.2 V (different code for low)
- Reference supply to some sensors: regulated ~5 V from PCM (verify on your model)
Diagnostic algorithm
- Retrieve freeze frame and live data; confirm P1198 and record signal voltage and engine conditions when fault set.
- Visually inspect sensor, connector, and wiring at radiator/coolant sensor for damage or corrosion. Repair any obvious issues.
- With ignition ON (engine off), backprobe the sensor connector: measure signal wire voltage and compare to reference and ground. If signal is near battery voltage, suspect short to 12V.
- Disconnect the sensor and measure the signal wire to ground and to battery positive. If signal still high with sensor disconnected, wiring short or PCM fault likely.
- Measure sensor resistance across its terminals and compare to spec at ambient coolant temperature. Replace sensor if out of spec.
- Check for proper reference voltage from PCM (if applicable) and ground continuity from sensor connector to chassis/PCM ground.
- Repair wiring shorts/open circuits or replace connector/sensor as indicated. Clear codes and road test to verify the fault does not return.
- If wiring and sensor are good and fault persists, suspect PCM input driver fault and consult factory procedures for PCM testing or replacement.
Likely causes
- Corroded connector at radiator temp sensor allowing intermittent high voltage
- Short between signal wire and ignition-switched 12V feed or battery positive
- Failed coolant temperature sensor (low resistance to 12V or open reference)
- Blown sensor ground or high-resistance ground connection
Fault status
Status
Radiator temperature sensor input voltage above allowable range detected by PCM. Possible short to battery, faulty sensor, wiring/connectors, or PCM input fault.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
Your experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
👍 Like
0
👎 Dislike
0
Send to email