Experiencing limp home mode in your vehicle can be frustrating, especially when accompanied by confusing OBDII codes. For Sprinter van owners, encountering charge pressure faults and the dreaded limp mode is a common issue. This article delves into a real-world troubleshooting journey focusing on the “Obdii Code Overboost” scenario, exploring the complexities of diagnosing intermittent turbocharger problems. We’ll analyze a step-by-step experience of chasing down boost issues, from underboost to overboost conditions, offering insights into potential causes and diagnostic paths.
Initially, the issue presented itself as intermittent limp home mode (LHM) activations in a 2005 T1N 3500 Sprinter van with 130,000 miles. The frequency of LHM occurrences escalated from occasional incidents during long trips to becoming alarmingly frequent, even triggering the malfunction indicator lamp (MIL). An initial scan using an Autel MD802 revealed a set of concerning codes:
OBDII Codes:
- P0299 Turbocharger/Supercharger underboost
- P2A00 O2 Sensor circuit range/performance
Sprinter Specific Code:
- The charge pressure control is faulty. Charge pressure too low.
The initial diagnosis pointed towards a boost leak, a common culprit for underboost codes. Despite the turbocharger sounding healthy and exhibiting minimal shaft play, the focus shifted to the intake and intercooler hosing. Suspecting leaks in the system, the hoses from the turbo to intercooler and the “elephant hose” (intercooler to intake manifold) were replaced. Additionally, a Dorman resonator was swapped out for an aluminum delete. During this process, the intake temperature sensor clips were unfortunately damaged, necessitating a temporary fix with duct tape before a replacement arrived.
This temporary fix proved to be short-lived. During a subsequent drive, the intake temperature sensor, secured only by duct tape, blew out of the elephant hose. This incident predictably triggered limp mode and the reappearance of the underboost codes. This confirmed the suspicion that boost leaks were indeed playing a role. Once a new temperature sensor was installed, the van seemed to recover, running smoothly without boost or O2 sensor codes for about a week.
However, the relief was temporary. While driving to Rhode Island, the Sprinter unexpectedly entered limp mode again, this time while climbing a gentle hill. Another scan with the Autel revealed a surprising shift in the fault code:
Sprinter Code: 2359-2: The charge pressure control is faulty. Charge Pressure is too HIGH.
The “obdii code overboost” condition had now emerged. The sudden transition from underboost to overboost was perplexing. Initial thoughts leaned towards over-tightened hose clamps, but further investigation into the turbo actuator rod revealed smooth, non-sticky movement. The actuator linkage appeared solid and responsive. Despite this, penetrating oil was applied as a precaution, and the codes were cleared.
The van once again resumed normal operation for another week before the intermittent limp mode returned. This time, the codes reverted back to the original underboost condition:
Sprinter Code: The charge pressure control is faulty. Charge pressure too low.
Restarting the van temporarily cleared the limp mode, allowing continued driving. However, the cycle repeated itself shortly after, with the system throwing an overboost code once more:
Sprinter Code: 2359-2: The charge pressure control is faulty. Charge pressure too high.
This back-and-forth between underboost and overboost conditions pointed towards a more complex issue than simple boost leaks. Several additional factors were considered during this troubleshooting process:
- EGR Valve: Attempts to clean the EGR valve were unsuccessful due to it being seized in the manifold. While no EGR-specific codes were present, the EGR system’s connection to charge pressure control raised suspicion.
- MAF Sensor and Air Filter: The air filter had been severely clogged and collapsed by a previous owner, potentially allowing unfiltered air to pass and contaminate the MAF sensor. While MAF signal readings seemed plausible on the Autel, the sensor’s condition remained uncertain.
- Turbocharger Behavior: During steady-state driving with cruise control engaged on inclines, the turbo exhibited erratic behavior, fluctuating between high and low speeds, mimicking gear changes despite the transmission remaining constant.
- Recent Turbo Replacement: The turbocharger assembly itself was a relatively new Garrett unit, replaced approximately 30,000 miles prior, seemingly reducing the likelihood of a complete turbo failure.
The fluctuating “obdii code overboost” and underboost conditions, combined with the turbo’s inconsistent behavior, suggest a potential issue with the charge pressure control system itself. While boost leaks were initially suspected and addressed, the intermittent and contradictory codes indicate a more nuanced problem. Potential culprits could include a sticking turbocharger actuator despite initial smooth movement checks, a malfunctioning MAF sensor providing inaccurate readings despite seemingly plausible data, or even issues with the EGR system impacting charge pressure regulation. Further investigation, potentially involving more in-depth diagnostics of the turbo actuator functionality under varying conditions, MAF sensor testing, and a more determined effort to address the EGR valve, is necessary to definitively resolve the root cause of these perplexing boost-related limp mode events.
