P0236-P0238 DiagnosticsA little background info on these codes:
These codes are in regards to the boost control circuit on 6.5TD built with OBD-II Capability.
Overboost, Underboost, and non responsive units will all set these codes.
To test the system follow these steps, and then post back with results.
This will work for F code engines, for S code the steps are the same, but you need to trace the EGR vacuum lines to ensure there are no leaks.
P0236 = Boost is 20 kPa or 2.9 PSI from PCM expectations at 1800-2400 RPM, under load.
P0237 = Boost is under 40 kPa or 5.8 PSI
P0238 = Boost is equal to or greater than 202 kPa Under 3506 RPM.
1. Check all battery connections and grounds. This is important as the PCM can do all kinds of weird things without proper grounding.
2. Check that you can freely move the waste gate actuator (mounted on the turbo with a vacuum line running to it)(remove vacuum line and move actuator while placing your finger over the vacuum port, you should be able to get suction and pressure)if you get no pressure/vacuum playing with the actuator, replace actuator.
3. Check the vacuum line running from the actuator to the solenoid(driver side of engine near intake manifold...has two vacuum lines, check these lines for any cracks or breaks, but be careful, it’s easy to snap them(in which case repair any vacuum lines as necessary).
4. Follow the vacuum line back to the vacuum pump, with the Belt off, see if you can turn the vacuum pump, you should feel resistance due to the pumping action. Also feel for grinding...any grinding or lack of pumping, suspect unit.
ENGINE RUNNING(belt replaced and hoses reconnected)
5. Check for vacuum at the solenoid. If you have no vacuum AT the solenoid and the vacuum line is good. Replace vacuum pump.
7. Check for vacuum coming OUT of solenoid(solenoid should activate and buzz when truck is idling)if no vacuum or solenoid not functioning. Replace solenoid.
8. Check for vacuum at actuator, if no vacuum at actuator, recheck vacuum lines.
Your MAP Sensor may be at fault, and is cheaper than the PCM. If mechanically/pressure wise everything is A-OK, Replace the MAP Sensor. NOTE:The Diesel MAP Sensor is different from the Gas MAP Sensor.
9. If you STILL can’t get the system working, the problem may be the PCM. Find a test unit(spare PCM) OR Order a Heath GL-4 and Turbo-Master(if you choose to upgrade, if you want to leave stock or have thrown a ton of parts at it...just get the GL-4/or a factory PCM)
This is just a guide, and you should post back your testing results BEFORE purchasing and replacing parts...we will help you along, and I hope you enjoyed reading my guide