A 2018 Jeep Renegade rolled into the bay with a check engine light, stuck in limp mode, and a single P023800 fault code stored in the engine control module. The technician working on this vehicle left a brief note detailing the customer complaint. They wrote, “La macchina va in emergenza e compare la spia motore”, which means the car goes into emergency mode and the engine warning light appears. This is a standard protective strategy. The engine control module cuts power to prevent internal damage when it loses trust in a critical sensor reading. In this case, the P023800 code points directly to the manifold absolute pressure sensor, or boost pressure sensor, indicating a circuit high condition.
High Voltage at the Boost Pressure Sensor
The most likely cause for this fault code on this specific vehicle is an internal failure of the MAP sensor. The diagnostic platform we build ranks this primary cause at a 45 percent probability with a high severity rating. The P023800 code means the engine control module detects a signal voltage from the boost pressure sensor that sits completely above the maximum calibrated threshold.
When a boost pressure sensor fails internally, it often shorts its own 5V reference voltage directly to the signal return wire. Inside the plastic housing, thermal cycling and vibration can break down the internal circuitry. The engine control module receives an artificially high voltage reading, interprets this as a short to a high circuit, and immediately triggers limp mode because it can no longer calculate actual boost pressure safely.
The testing path for an internal sensor fault starts before you even open the hood. The technician is guided to monitor live data from the MAP sensor with the key on and the engine off. This key-on state is crucial. The sensor should read normal atmospheric pressure when the engine is not running. If the scan tool shows a maximum pressure reading while the engine is stationary, the circuit clearly has a problem. To isolate the fault to the sensor itself, the technician disconnects the MAP sensor plug. If the live data voltage drops immediately upon disconnection, the wiring is fine and the sensor itself has failed internally.
Electrical Shorts on the 1.6 MultiJet Harness
If disconnecting the sensor does not drop the voltage, the diagnostic path moves to the wiring harness. We rank a short to a power source in the MAP sensor wiring as the second most likely cause, sitting at a 30 percent probability with a high severity rating.
The 1.6 MultiJet engine in this Renegade is particularly vulnerable to wiring damage in areas exposed to high vibration or elevated temperatures. The signal wire for the boost pressure sensor can chafe against the engine block or adjacent metal brackets. Once the insulation wears through, the exposed signal wire can make contact with a 5V reference wire or a 12V battery feed. This sends maximum voltage back to the engine control module, triggering the exact same P023800 code as an internal sensor failure.
Our suggested test for this stage involves probing the electrical circuit at the connector. The technician checks the voltage, ground, and signal pins for correct values using a multimeter. A complete visual inspection of the harness routing is necessary, looking for spots where the loom rubs against hard edges. The technician follows this with a wiggle test, physically moving the harness while watching live scan tool data to see if the voltage spikes when a chafed wire touches a power source.
There is another electrical fault that can trigger a circuit high code, which our data ranks at a 10 percent probability with a medium severity rating. This is a short to ground or a poor ground connection on the MAP sensor circuit. While a P023800 code specifically means the circuit is high, a failing ground can cause the signal voltage to float artificially high. If the resistance on the ground circuit increases due to corrosion in a connector or physical wire damage, the engine control module receives an erratic, elevated reading.
The testing procedure here requires a continuity test of the MAP sensor ground circuit. The technician checks the electrical circuit at the connector, specifically looking for unwanted voltage on the ground pin. If the ground is floating, a voltage reading will appear where there should be none, confirming the harness is at fault.
Ruling Out Mechanical Overboost
A P023800 code is almost always an electrical circuit fault, but there is a mechanical outlier that technicians must keep in mind. We rank excessive mechanical overboost at an 8 percent probability with a high severity rating.
In rare cases, a physical malfunction in the turbocharger system can cause the actual manifold pressure to exceed the physical measuring limit of the MAP sensor. If the wastegate gets stuck closed, or if the boost control solenoid fails to regulate pressure, the turbocharger will build maximum boost. The sensor reads this extreme pressure and outputs its maximum possible voltage. The engine control module sees this constant maximum voltage and flags it as a circuit high error, assuming the sensor must be broken when in reality it is just reading an extreme mechanical event.
Testing for mechanical overboost requires a different approach because the static electrical tests will all pass. The technician must analyze live data while the vehicle is under load. By comparing the desired boost pressure requested by the engine control module against the actual boost pressure measured by the sensor, the technician can see if the turbocharger is over-pressurizing the intake. A physical test of the wastegate actuator is also required to confirm the mechanical components are moving freely and not binding under exhaust heat.
Taking the Next Step
Every diagnostic path requires a logical sequence of tests to prevent replacing parts that are actually functioning perfectly. We see wiring harness chafing on these 1.6 MultiJet engines frequently in our own data, forcing technicians to chase electrical ghosts. Take a look at your own repair orders for this engine family. Are you seeing more sensor failures, or are harness repairs becoming the standard fix in your bays?
Reference pages for the codes in this article
- P0238, what we measure for this code across real diagnostics
