Problems Encountered

Various issues encountered over the years, with descriptions and answers

Reader's Guide

Problems are marked in italics.
Confirmed solutions are highlighted.
Diagnostic hints are marked in bold green.
#npf is a situation where no problem was actually found.
Pink highlighting indicates a problem that was clearly duplicated, but for which no solution is yet known.

Prius with several codes

Vehicle has separate/unrelated issues in two systems. Neither are related to TSB 003-21 provided by customer (inverter IPM failure).

- P148F, P261B indicate water pump/cooling system related faults. Water pump speed is maxed out even with full coolant, indicating a failed impeller. Engine overheats. Possible internal engine damage due to overheating. Need to replace water pump in order to determine if engine can properly maintain temperature. Strong possibility of head gasket failure. Diagnostic time includes replacement of water pump and coolant, identification of cause of coolant loss. Separate time would be required to repair the cause of the coolant loss (head gasket, exhaust coolant valve, or just normal evaporation).

- P0441, P0455 evap purge flow, gross leak. Purge valve does not open. Leak detection test is unable to operate. Self-test will not advance past the initial reference check at this time. Suspect charcoal canister leak detection pump failure. Need to replace purge valve in order to diagnose leak detection failure, then the large leak (P0455) will have to be located and repaired. Diagnostic time includes replacement of necessary valves, smoke and vacuum tests, but would require additional time to repair any system leaks once they are identified.

2GR Piston Slap, Other Noises

Engine noise on startup - only noise noted was typical 2GR piston slap noise - noise goes away when engine warms up - normal operation

Rear suspension noise: only noise noted during test drive sound like tire/bearing noise. Tires were rotated and no change was noted. Checked bearings individually on lift and none of the wheel bearings made any noise - loudest part of drivetrain was rear differential. No other potential bearing issues were noted during inspection. -- replace rear differential unit

Front end noisenoise noted from steering column. All column bolts are tight. Suspect intermediate shaft noise, slight knocking is felt in the lower part of intermediate shaft when steering wheel is moved around. No saftey issues noted, light noises from these shafts are typical at this vehicles age/mileage. Replace intermediate shaft and align front end.


C1391 - Brake booster accumulator leaking - per service bulletin, booster, master cylinder, and skid control ECU update are required.

Engine running rough, window stuck down

Engine running rough: no communication initially with ECM, alarm hooked into OBD connector; repaired wiring and confirmed communication with ECM. dead misfires in at least one cylinder. Identifed failed #4 and #6 coils.

check engine light is being commanded on, but does not come on. other lights on dash turn on with active test, no active test for MIL is available. MIL is a LED built into the dash cluster, not a replaceable bulb. Need to check wiring at cluster. codes stored indicating that the engine is incorrectly timed. need to replace timing belt to start - engine damage may have already occured but is not apparent in current condition.

RR window: master window switch is shorted, forcing the RR window down at all times. RR window switch was unplugged to prevent this. Window is currently stuck down. Need to replace master window switch.

Noises, Diagnostic Procedure

noise from LF over bumps:
-- checked vehicle prior to service and noted squeak noise over bumps at all speeds
-- retorqued body mounts, under shield bolts, greased bushing surfaces
-- rechecked vehicle after service and no noise was noted
-- small amount of noise was noted when vehicle was rocked in parking space. some noise is normal and to be expected with this vehicle's mileage. further noise reduction would require replacement of suspension components, including variable-lift shocks and sway bar bushings. no safety concerns or loose components were noted during inspection.

Note: for trucks, check body mounts, which create a squeak noise when rocked while parked and over bumps. Body mounts can be tested by loosening all six, slightly raising the body to relieve pressure, then lowering it and tightening the mounts again.

Failed Head Gasket

Multiple issues relating to the check engine light:

- P148f - engine coolant pump over-revolution - reservoir empty. diagnostic time used to determine over-revolution condition (this code can indicate an air pocket in the coolant caused by a failed catalyst diverter valve, leaking head gasket, or a failed engine water pump)
- P0302 - misfire in cylinder #2 - freeze frame data shows that the engine was at normal operating temperature (180F) when the code set. vehicle also had a hard misfire upon startup. could be related to coolant condition if the coolant condition is caused by a failed head gasket. separate diag. time would be necessary to remove cowling and check ignition and fuel delivery systems if no head gasket leaks are found.

----- Heavy misfires on startup - temperature stays at 200 deg., significant gas loss through coolant reservoir - coolant becomes cloudy, fans will not activate. engine water pump operates normally when coolant reservoir was filled, both with active test and during normal engine operation. head gasket has failed and several maintenance items are recommended while the engine head is off the vehicle.

Questions about Fuel Economy

Customer states fuel economy has dropped "quite a bit." Customer states fuel economy went from an average of 35 to 30 mpg.

No codes present in health check. Knock correction learn value is 18 deg (normal), fuel trims were neutral during entirety of 10 mile test drive while in closed loop. No change in displayed calculated value during test drive (30.6 mpg). EPA estimate for this model, per, is 27 mpg city, 34 mpg hwy, 30 combined, a min-max range of 23% of average.

Potential Issues Noted: Customer has one tire with a large leak (LF) which was at 15 psi upon arrival, and one tire RR that does not appear to be damaged, but was low (25 psi), which, along with cold weather and increased need for vehicle to operate at open loop in order to reach operating temperature, can negatively impact fuel economy. Test drive was done with tires set to correct pressure.

Vehicle has an aftermarket (Curt) tow hitch installed; towing can reduce fuel economy.

Vehicle is serviced at Jiffy Lube; use of heavier lubricants can reduce fuel economy. No record of service is available for access by the dealership.

Questions about Shifting

Customer states transmission is not shifting correctly, mentioning that there is no kickdown when attempting to accelerate from 30+ mph. Unable to duplicate customer concern. Vehicle is equipped with 8 speed automatic transmission. Depending on learned shift values and customer input to throttle as well as VSS input to transmission control computer, vehicle may have to shift through multiple gears to reach an engine speed appropriate to customer demand. No unusual driving conditions noted, no TSBs present, no codes noted in health check. Reset to factory defaults is not recommended without a transmission replacement, as it can result in unexpected behavior. No recommendation can be made regarding the transmission.

Pre-collison (PCS) Light

Malfunction lights on dash relating to precollision system, radar cruise, park assist, and front recognition camera. All codes except for park assist codes were related to a blown fuse for the millimeter wave radar sensor, which cut communication between MWRS and all other ECUs. replaced the fuse and completed the calibrations necessary when the system is reset, including distance and lane departure systems.

Park assist codes were related to a disconnected park assist radar wire. reconnected radar wire and completed angle measurements for individual sensors, programming of angles into ECU, and steering angle sensor calibration.

Auto-Access Seat

customer states vehicle will not come out of park because auto-access seat will not lock in place. unable to duplicate through several cycles. only time vehicle would not come out of park is if the auto access seat had not been fully returned by the operator to the initial (retracted) position. cycled lift 10 times and confirmed that the seat was locked with a confirmation beep; each time, the vehicle went out of park normally. customer will want to confirm that they are hearing the confirmation beep for the seat before attempting to shift out of park, rather than a confirmation from something else (the same beep is used for doors, etc.). no recommendations for repair can be made.

Noise on Startup

slightly higher rev from engine on initial startup occasionally due to low oil pressure (reduced resistance to starting), coupled with a slight knock/rattle from the engine. this is a common condition and does not impact engine performance. an updated cam gear is available to reduce overnight pressure loss, but is not required for the engine to continue to perform normally. note also, oil level was over 2 qts. low, engine may be consuming oil. Rec. replace timing chain (including resealing timing cover) as a maintenance item while cam gear is being replaced.

Door ajar light comes on going around turns

confirmed condition, RR door switch shows that the door is open when making left turns. swapped door courtesy switches and condition stayed on RR side. noted that condition was able to be duplicated when pressing on the back interior of the door panel. taped a rubber spacer to the sliding door body and condition was resolved. vehicle needs to be sent to a body shop for an estimate on repairing the fit of the door to the body. no factory remedies are available, as the vehicle is a heavily modified rampvan.

SRS light is on, codes are present for driver's seatbelt and driver's seat squib; all components are plugged in and fed into a modified rampvan wiring harness, which we do not have wiring diagrams for. Component failure would have to be diagnosed by a mobility van specialty shop. Codes B1656, B1826.

Oxygen sensor heater codes

MIL on, two codes present for both upstream (bank 1 and bank 2) oxygen sensor heater circuits being open. Confirmed that both sensors share a 20A fuse and relay and that neither was getting voltage from the harness. Removed fuse block cover and found 20A AF HTR fuse to be missing. Installed new fuse and confirmed voltage. Test drove vehicle to run monitors and found that the heater sensor tests completed and passed. Suspect customer removed AF HTR fuse at some point. vehicle has extensive aftermarket and nonstandard wiring in engine bay and throughout vehicle to power accessories. No guarantee can be made regarding the integrity of the additional wiring and accessories; future wear, short circuits, etc. may result and would be unrelated to today's repair. At least one aftermarket lamp was observed to have water in it (on left rear corner of roof).

Head gasket problems, misfires on cold start

Customer has misfires in cylinders 1 & 2. Several pieces of circumstantial evidence suggest that there is a head gasket problem:

- The customer had a similar problem about 10k ago, when the weather was cold.
- The misfires are in adjoining cylinders.
- The misfires that were recorded happened at a low air temperature shortly after starting up.
- The coolant reservoir is nearly empty.
- No misfires are occurring currently.

Gas Cap

MIL on - customer has codes for a large evap leak. Customer has aftermarket gas cap on vehicle. Gas cap was tightened and system was pressure/vacuum tested (test results attached to hard copy), confirming there were no other leaks. Suspect customer either left aftermarket gas cap loose, or replaced the gas cap because the factory one indicated a leak.

TRAC light

C/S TRAC light on. Unable to duplicate traction control light condition. Wheel bearings are not noisy while driving; customer concern is typically associated with a wheel bearing failing, but no evidence of that is present yet. One ABS code stored for abnormal steering angle sensor angle, and steering wheel is off-center. Rack was replaced at some point. In the absence of any other information, rec. align vehicle and complete steering angle sensor recalibration in case traction control is being activated by an unexpected steering angle input. Additional work may be necessary, but no indication of the condition described by customer is present.

MIL - VIN mismatch, Oxygen Sensor Problem

Customer has codes stored for P0606, P0138, and P0630. Customer requests to have the VIN programmed for the new ECM. NOTE - P0606 sets when P0138 is present due to how the oxygen sensor wiring is set up. If the oxygen sensor problem is not addressed, the MIL and P0606 will return even after the ECM has been replaced and the new VIN has been programmed. Check engine light is off right now because it clears automatically when the VIN is programmed, but it is expected to come back on. Vehicle appears to have the original oxygen sensor and a large exhaust leak that was patched with exhaust cement. Rec. repair exhaust leaks and replace oxygen sensor in order to prevent a return of the check engine light. Also - vehicle has an extended crank time, which is typically associated with fuel pressure issues. These would have to be addressed after the oxygen sensor concern is addressed to ensure that the fuel trims are being read correctly.

Hybrid Shift Issue

C/S vehicle shifts abnormally. Vehicle has a hybrid CVT and does not operate using a traditional fixed-gear system. No unusual shifting conditions noted on 4 mile test drive. No codes present in system when health check was done after test drive. Suspect customer may have felt an appropriate transmission response based on previous learned values, applied in an unfamiliar drive setting. No recommendations can be made.

Sunroof Leak

Sunroof drip tray is flooded and clogged with mud - rec. clear out drip tray and run auger through sunroof drains. Strongly recommend for customer to remove the add-on wind deflector over the sunroof. Wind deflector is blocking the wind that would be otherwise blowing away debris and allowing the debris to crumble and fall into the drip tray. Sunroof drains are now clear and water flow was confirmed when tested.

MIL - Transmission Solenoid Issue

- Check engine light is on, code stored for transmission solenoid "a" failure. Followed repair manual procedure and confirmed 14.6 ohms resistance at the transmission wire and at the ECM wire, indicating an ECM failure; however, when code was cleared, the code did not return immediately, indicating that the ECM is working normally internally. Code did not return on 4 mile test drive. Suspect that there may debris or wear causing incorrect operation of solenoid in the valve body, and the computer is misinterpreting this failure to activate as an electrical circuit failure.

- Rec. flush transmission fluid as a preliminary measure to clear out any potential loose debris. Evidence suggests that if the code returns, the valve body has been compromised and the transmission would need to be replaced. Current conditions make it impossible to confirm this. Labor for transmission flush is separate from diagnostic time used to confirm wiring between ECM and transmission wire/solenoid.

TRAC light

When accelerating at WOT, traction control light flashes intermittently and acceleration is lost. No obvious differences in wheel speed when snapshot is taken, no codes stored, ABS does not activate. Front tires are 205 55 16 (correct size), rear tires 205 65 16. Case created to confirm tire size difference could cause this condition. per engineer, the slight difference in acceleration from the rear tires during heavy accel/WOT was enough for the ECM to perceive the difference as a slip and activate the traction control, but during regular cruising, the difference in the tires is close enough to behave normally and not set a code. need to replace the rear tires to size 205 55 16 to match the fronts.

Thermostat Opens Early

Vehicle was previously diagnosed with a thermostat which is opening early. same code is present with same symptoms. no unusual shaking noted while test driving or at idle; idle speed is normal (~800 rpm). code in system results only in reduced fuel economy due to engine having to run at full rich for a longer period of time (as engine cannot reach operating temperature)

Tire Pull

Slight pull noted during initial test drive. only a small adjustment to RF wheel was required during alignment; adjusted tie rods to be in spec and no change was noted during second test drive. Outcomes suggest that the pull is coming from the tires themselves and not the alignment. rec. start by cross-rotating tires to inspect for change in pull. next step would be to replace tires. tire manufactured in 2018. tread depth between 7 and 9 32nds between all four tires.

Blower Motor - Intermittent Operation

Customer states blower motor intermittently only operates on high. Blower motor connector B3 was redone; blower motor resistor was replaced in 20--. One wire going to the resistor is burned and causing an intermittent open. An updated TSB relating to this concern was introduced in 2021, which includes updated repair parts. replaced resistor, repaired wiring, confirmed correct operation


P0128 - thermostat is opening early or hanging open after shutoff. rec. replacement of thermostat, gasket, and coolant.

Fuel Pump Noise

customer thinks the fuel pump is continuing to run after the vehicle is turned off. notes that he heard the noise multiple times while the vehicle was in his garage. no unusual noises noted during multiple start/shutoff cycles. fuel pump starts and stops normally. suspect customer may be hearing the operation of the evap vacuum pump, which is located behind the fuel tank (under the truck bed) and periodically activates to test for leaks in the fuel tank, charcoal canister, and other evaporative emissions system components. normal pressure bleed noise relating to direct injector rail noted after engine cutoff.


MIL on - P0705 Park/Neutral Input: shifter is very tight. disconnected shifter from transmission and found shifter lever moves easily. observed heavy rust on the mounting bolt for the park/neutral switch on the transmission. heavy rust under vehicle. suspect corroded park/neutral switch internals and recommend replacement of park/neutral switch.

Refrigerant Leak

Previous notes show AC system output at 45 deg. after evac/recharge/addition of dye. Current AC system pressures are at 20 PSI, indicating that the system has a leak. Dye was observed in the low side charging valve. No obvious points of leakage. Only suspicious areas were the inlets for the rear AC pipes (possible leaking O-ring) or from the front evaporator. Rec. start with replacement of rear AC line O-rings, evac, recharge, and add dye. Continued leakage would confirm a failed evaporator.

Defroster Inoperative

Customer states upper section of defroster is inoperative. Rear defroster turns on and operates normally; has normal voltage drop across the length of the grid (battery voltage gradually dropping to zero). NOTE - upper grid is the radio antenna, not a defroster.

Noise while in motion

Only noise noted while test driving was coming from tires; tires have decent tread but are in rough condition, noise is more evident during braking as the vehicle weight shifts to the front. cupping of tires caused by weak shocks/struts. rec. replacement of tires, shocks, and struts (alignment required); tires to address noise, shocks/struts to reduce further incidence of noise. Vehicle has rough idle feel due to collapsed engine mount.

Rear Seat Belt Light

If any weight is detected in the rear seat without the seatbelt being fastened, the group of lights will illuminate and then turn off after 30 seconds of no weight being detected, including when the vehicle starts initially. No weight sensor adjustment can be made.

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