ProjectSeahorse
Member
Car has about 235,000 miles. I bought it about 10 months ago with 220k miles. During maintenance, I found the MAP sensor wiring was improperly routed, and was rubbing against the serpentine belt. The insulation was worn in one area on all 4 wires, exposing bare wire, but the wires were all intact- no broken or missing wire strands. I went ahead and individually wrapped the wires with electrical tape, tucked them back into the wire loom, and routed them as they should be. All was well for 15,000 miles.
A few weeks ago, the car went into limp mode, very low power. CEL was on with code P0652, "Sensor reference voltage 'B' circuit low". Looking at live data I could see that the manifold absolute pressure was reading static at 19 kpa, even when engine was not running (atmosphere should be 101 kpa or 29.92inhg, approximately...). I bought a new bosch MAP sensor, and it immediately read 101 kpa with the engine off, atmospheric pressure. Kpa increased with throttle/boost. Code cleared, all good, normal boost for 2 weeks and a few hundred miles. The old sensor was coated in oil, as I do have a good amount of oil which seems to be coming from the crank case ventilation and contaminating the intake. I assumed this is what killed the old sensor. As a precaution, I rechecked the 4 wires as far as I could (until they disappear into wire loom with other harnesses etc), to be sure they weren't shorting to each other or something else. All appeared ok.
Well, a couple of weeks and a few hundred miles later, the car goes back into limp mode, same code, and the new MAP is reading 40 kpa and is stuck there no matter what the engine is doing. I pulled the sensor, and it appears visually clean, though I'm sure there could be a very thin oil film. I cleaned the sensor just in case with isopropyl alcohol (not sure what the appropriate cleaner is, but figured I'd be buying a new sensor anyways, and wanted to see if the value changes).
I'm not sure if I should be pursuing an electrical issue taking out the sensor, or oil contamination. I couldn't imagine that a non-visible oil film would immediately cause catastrophic damage to the MAP sensor, but could it? Is there a source for what voltages I should be seeing from the ECU to the sensor? I assume I should check each wire to ground, and continuity between each wire- Do I need to unplug ECU for this? I thought I saved the old sensor, as I wanted to compare ohm readings, but I can't find it. Is there a chart for ohm values of the sensor? At this point, I plan on replacing the CCV and cleaning the intake, then throwing another sensor at it, but hate to start a habit of routine sensor replacement if it's not the issue.
Thanks for any insight
A few weeks ago, the car went into limp mode, very low power. CEL was on with code P0652, "Sensor reference voltage 'B' circuit low". Looking at live data I could see that the manifold absolute pressure was reading static at 19 kpa, even when engine was not running (atmosphere should be 101 kpa or 29.92inhg, approximately...). I bought a new bosch MAP sensor, and it immediately read 101 kpa with the engine off, atmospheric pressure. Kpa increased with throttle/boost. Code cleared, all good, normal boost for 2 weeks and a few hundred miles. The old sensor was coated in oil, as I do have a good amount of oil which seems to be coming from the crank case ventilation and contaminating the intake. I assumed this is what killed the old sensor. As a precaution, I rechecked the 4 wires as far as I could (until they disappear into wire loom with other harnesses etc), to be sure they weren't shorting to each other or something else. All appeared ok.
Well, a couple of weeks and a few hundred miles later, the car goes back into limp mode, same code, and the new MAP is reading 40 kpa and is stuck there no matter what the engine is doing. I pulled the sensor, and it appears visually clean, though I'm sure there could be a very thin oil film. I cleaned the sensor just in case with isopropyl alcohol (not sure what the appropriate cleaner is, but figured I'd be buying a new sensor anyways, and wanted to see if the value changes).
I'm not sure if I should be pursuing an electrical issue taking out the sensor, or oil contamination. I couldn't imagine that a non-visible oil film would immediately cause catastrophic damage to the MAP sensor, but could it? Is there a source for what voltages I should be seeing from the ECU to the sensor? I assume I should check each wire to ground, and continuity between each wire- Do I need to unplug ECU for this? I thought I saved the old sensor, as I wanted to compare ohm readings, but I can't find it. Is there a chart for ohm values of the sensor? At this point, I plan on replacing the CCV and cleaning the intake, then throwing another sensor at it, but hate to start a habit of routine sensor replacement if it's not the issue.
Thanks for any insight
