My 98 sonoma 2.2L truck has wanting to surge on its own while going anywhere between 45 to 70 mph. I just had the transmission looked at, they said all is good. I was told to replace the TPS sensor which I did, and the problem is still occuring. It just seems like the truck engine wants to surge on it's own. The RPM's will be at a steady 2000 then all of the sudden they will jump to 3300 and right back down. I do not have any other clues to what it could be. I'm going on a road trip for memorial day weekend and I need it fixed. PLEASE HELP!!! IM DESPERATE NOW.
Flares, Erratic Shifts and Intermittent Concerns, DTC P1811 or P0748 Set (Replace Pressure Control Solenoid Valve Assembly)
Before guessing at transmission problems, check the fluid level (car warmed up, engine running in Park on level ground) and have the PCM scanned for trouble codes FIRST.
Put a line pressure gauge (J 21867 Universal Pressure Gauge Set or visit a local trans shop) on the pressure test port and go for a drive to verify proper line pressure. Base pressure at idle in P,N,OD should be around 70psi and around 140psi in R. Max line pressure should be at least 190psi at WOT in 1st or 2nd, 225psi is optimum. If base pressure is low, trans or pump is worn out. If max pressure is low, check EPC solenoid. If reverse is slow to engage, and line pressure does not come up to at least 130psi in reverse, replace the boost valve with a Transgo 0.490" Stock was 0.470" or 0.420" boost valve (easy fix in pan).
Important: Before performing a line pressure check, verify that the pressure control (PC) solenoid valve is receiving the correct electrical signal from the PCM.
1. Install a Scan Tool.
Caution: Keep the brakes applied at all times in order to prevent unexpected vehicle motion. Personal injury may result it the vehicle moves unexpectedly.
2. Start the engine and set the parking brake.
3. Check for a stored Diagnostic Trouble Code (DTC).
4. Repair the vehicle, if necessary.
5. Check the fluid level. Refer to the Transmission Fluid Checking Procedure.
6. Check the manual linkage for proper adjustment.
7. Turn the engine OFF. Remove the oil pressure test hole plug and install the J 21867.
8. Put the gear selector in PARK range and set the parking brake.
9. Start the engine and allow the engine to warm up at idle.
Notice: Total test running time should not be longer than two minutes, or else transmission damage could occur.
10. Access the PC solenoid valve control test on the Scan Tool.
11. Increase the PC solenoid as shown actual current from 0.0 to 1.0 amps in 0.1 amp increments. Allow the pressure to stabilize for five seconds after each pressure change. Read the corresponding line pressure on the J 21867.
12. Refer to the Line Pressure specification table. Compare the data to the table.
13. If pressure readings differ greatly from the table, refer to Incorrect Line Pressure.
14. Remove the J 21867.
15. Apply sealant, P/N 12345382 (in Canada, P/N 10953489), to the oil pressure test hole plug.
Notice: Refer to Fastener Notice in Cautions and Notices.
16. Install the oil pressure test hole plug. Tighten the oil pressure test hole plug to 12 N.m (106 lb in)
Some owners of vehicles with 4L60E may comment on harsh upshifts or harsh garage shifts, soft shifts, shudders on hard acceleration, or shifts erratic. These conditions may appear intermittently or set a DTC P1811 or P0748. During diagnosis, a low or high line pressure (actual versus desired) may be observed.
The above condition may be due to any one of the following which may affect line pressure output:
Sediment inside the pressure control (EPC) solenoid valve, causing the EPC solenoid valve to mechanically bind.
Sediment in the valve body, causing the torque signal regulator valve to stick.
Incorrect transaxle oil level.
Important: Any of the above conditions may be intermittent, therefore, this test should be performed at least three times.
Refer to the Line Pressure Check Procedure in SI, along with the Line Pressure Specification Table shown, to determine if actual versus desired pressures are within the values specified. The Scan Tool is only able to control the PC solenoid valve in PARK and NEUTRAL with the vehicle stopped. This protects the clutches from extremely high or low pressures in DRIVE or REVERSE ranges.
Refer to the Line Pressure Specification Table mentioned above or from the transmission shop for the 4L60E. The pressures in the table assume a temperature of 70°C. The pressure will vary with a change in temperature.
If the actual versus desired pressures are not within the values specified, clean the valve body and replace the EPC solenoid valve, if necessary.
Check the EPC solenoid valve actual versus desired pressures to verify the new EPC solenoid valve is responding correctly.
EPC (Electronic Pressure Control) valve.
#377 is your EPC valve and you don't have to drop your valve boday to replace it but you do have to drop the transmission pan.
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