What is Caterpillar Fault Code SPN167?

SPN 167 indicates a problem with the Charged Air Cooler (Aftercooler) Temperature sensor circuit. This fault code means the Electronic Control Module (ECM) has detected an abnormal voltage signal from the temperature sensor monitoring the air exiting the aftercooler before it enters the engine's intake manifold.

The Charged Air Cooler (also called an aftercooler or intercooler) reduces the temperature of compressed air from the turbocharger, increasing air density for better combustion efficiency. The temperature sensor provides critical data to the ECM for fuel injection timing, air-fuel ratio calculations, and engine protection algorithms. On Caterpillar excavators, this sensor typically uses a thermistor-type design with resistance that changes with temperature. When SPN167 activates, the ECM loses accurate intake air temperature data, potentially causing reduced performance, increased fuel consumption, or engine protection derates.

Common Symptoms

• Check Engine Light or Malfunction Indicator Lamp (MIL) illuminated on the instrument cluster
• Engine derate or power reduction, especially under heavy load conditions
• Black smoke from the exhaust due to improper air-fuel mixture calculations
• Poor throttle response or hesitation during acceleration
• Reduced fuel efficiency as the ECM defaults to conservative fuel maps without accurate temperature data

Potential Causes

The most common technical failures causing SPN167 in used Caterpillar excavators include:

• Damaged or corroded wiring harness at the sensor connector or along harness routing points where cables rub against frame components
• Failed aftercooler temperature sensor due to age, thermal cycling, or internal thermistor degradation
• Moisture intrusion into the connector terminals causing short circuits or high resistance connections
• Chafed wiring near the turbocharger or exhaust components where heat has degraded insulation over time
• Poor ground connections at ECM or chassis ground points creating erratic voltage readings
• ECM internal circuit failure (less common but possible in high-hour machines)

How to Troubleshoot and Fix Code SPN167

Step 1: Visual Inspection Begin by thoroughly inspecting the aftercooler temperature sensor and its wiring harness. The sensor is typically located on the intake manifold or charged air piping between the aftercooler and engine. Check for damaged connectors, corrosion on pins, cracked sensor housings, or obvious wire chafing. On used excavators, pay special attention to harness sections near moving components or heat sources where insulation may have deteriorated over thousands of operating hours.

Step 2: Electrical Testing Using a digital multimeter, disconnect the sensor and measure resistance across the sensor terminals at various temperatures (compare readings to manufacturer specifications—typically 2,000-10,000 ohms depending on temperature). Check for supply voltage at the harness connector (usually 5 volts from the ECM). Test for continuity from the sensor connector back to the ECM pins to identify open circuits. Inspect ground integrity by measuring resistance from sensor ground to battery negative (should be less than 5 ohms).

Step 3: Advanced Diagnostics Connect Caterpillar Electronic Technician (Cat ET) diagnostic software to view live sensor data and compare actual temperature readings against expected values. Check for intermittent connections by wiggling the harness while monitoring voltage signals—fluctuations indicate poor connections. On older machines, remove connectors and apply dielectric grease after cleaning corrosion with electrical contact cleaner. If all circuits test properly but the code persists, replace the temperature sensor with a genuine Caterpillar part to ensure proper resistance curve matching for ECM calibration.

Step 4: Verification After repairs, clear fault codes using diagnostic software, run the engine through various load conditions, and verify the code does not return. Monitor aftercooler temperature readings to confirm they respond appropriately to operating conditions.

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Disclaimer: This guide provides general diagnostic information for SPN167 on Caterpillar excavators. Always consult the specific service manual for your machine model and serial number. If you lack proper diagnostic tools or experience with heavy equipment electrical systems, seek assistance from a certified Caterpillar technician to prevent further damage.